tutorial c#

.Net Framework and C#

By: Vikas Srivastava, Department of Computer Applications, JSSATEN 1

1. What is .NET?

It is a platform neutral framework.

It is a layer between the operating system and the programming language.

It supports many programming languages, including VB.NET, C# etc.

.NET provides a common set of class libraries, which can be accessed from any .NET based programming language. There will not be separate set of classes and libraries for

each language. If you know any one .NET language, you can write code in any .NET language!!

In future versions of Windows, .NET will be freely distributed as part of operating system and users will never have to install .NET separately.

2. What is Not?

.NET is not an operating system.

.NET is not a programming language.

3. ".NET is a framework"

Confused with this definition?

We cannot define .NET as a 'single thing'.

It is a new, easy, and extensive programming platform.

It is not a programming language, but it supports several programming languages.

By default .NET comes with few programming languages including C# (C Sharp), VB.NET, J# and managed C++.

.NET is a common platform for all the supported languages. It gives a common class library, which can be called from any of the supported languages.

So, developers need not learn many libraries when they switch to a different language. Only the syntax is different for each language.

When you write code in any language and compile, it will be converted to an 'Intermediate Language' (Microsoft Intermediate Language - MSIL).

So, your compiled executable contains the IL and not really executable machine language.

When the .NET application runs, the .NET framework in the target computer take care of the execution. (To run a .NET application, the target computer should have .NET framework installed.)

The .NET framework converts the calls to .NET class libraries to the corresponding APIs of the Operating system.

Whether you write code in C# or VB.NET, you are calling methods in the same .NET class libraries.



The same .NET framework executes the C# and VB.NET applications.

So, there won't be any performance difference based on the language you write code.

3.1 Is it platform independent?

Many people ask this question "Java is platform independent, what about .NET?”. The answer is "Yes" and "No”!

The code you write is platform independent, because whatever you write is getting compiled into MSIL.

There is no native code, which depends on your operating system or CPU. But when you execute the MSIL, the .NET framework in the target system will convert the MSIL into

native platform code.

So, if you run your .NET exe in a Windows machine, the .NET framework for Windows will convert it into Windows native code and execute.

If you run your .NET application in Unix or Linux, the .NET framework for Unix/Linux will convert your code into Unix/Linux native code and execute.

So, your code is purely platform independent and runs anywhere!

But wait, we said it wrong... there is no .NET framework for UNIX or Linux available now.

Microsoft has written the .NET framework only for Windows.

If you or some one else write a .NET framework for other platforms in future, your code

will run there too. So, let us wait until someone write .NET framework for Linux before you run your .NET code in Linux.

3.2 Major Issues before .NET

Registration of COM components.

Unloading COM components

Versioning Problem (DLL Hell) The .NET Platform

The .Net platform is a set of technologies. Microsoft .NET platform simplify software development (Windows or WEB) by building applications of XML Web services.

The .NET platform consists of the following core technologies which are refer as components of .NET: -

The .NET Framework

The .NET Enterprise Servers

Building block services

Visual Studio .NET A programming model (.NET framework) enables developers to build Ex tensible Markup

Language (XML) Web Services and applications.



The .NET Platform Architecture

3.3 Components of .NET Framework

The .Net Framework consists of:

Common Language Runtime

Class Libraries

Support for Multiple Programming Language

Components of .NET Framework

.NET Compliant

Languages (VC++, VB.NET,

ASP.NET, C# and

other third party languages)

Common Language Runtime

(Memory Management, Common Type System, Garbage Collector)

Windows Forms Web Forms

Web Services

.NET Framework Base Class Library

(ADO.NET, XML, Threading, Diagnostics, IO, Security, etc.)

Developer Tools .NET Framework

Application

Libraries

CLR

.NET

Enterprise Servers

.NET

Building Block

Services

C#, Visual Basic .NET

Visual Studio .NET

Windows OS (Win 32)



4. Application Development and Execution

.NET is a multilingual platform then any .NET based language can be chosen to develop applications.

4.1 Choosing a Compiler According to the language we can choose its run time aware compiler for .NET platform. Because it is a multilingual execution environment, the runtime supports a wide variety of data types and

language features. 4.2 Compiling to MSIL

Source code to native code and code execution

When compiling source code, the compiler translates it into an intermediate code represented in MSIL. Before code can be run, MSIL code must be converted to CPU-specific code, usually by a

just-in-time (JIT) compiler. When a compiler produces MSIL, it also produces metadata. Metadata includes following information: -

Source Code

Compiler

Class Libraries

(IL & Metadata)

EXE/DLL (IL &

Metadata)

Class loader

Security

checks

Managed

Native Code

Execution

JIT Compiler

Runtime Engine

Call to an uncompiled method

Trusted pre-

JIT code only



Description of the types in your code, including the definition of each type.

The signatures of each type’s members,

The members that your code references.

Other data that the runtime uses at execution time. The MSIL and metadata are contained in a portable executable (PE) file that is based on and

extends the published Microsoft PE and Common object file format (COFF) used historically for executable content. The file format, which accommodates MSIL or native code as well as metadata, enables the operating system to recognize common language runtime images.

4.3 Compiling MSIL to Native Code

Before you can run Microsoft intermediate language (MSIL), it must be compiled against the common language runtime to native code for the target machine architecture. The .NET Framework provides two ways to perform this conversion:

•A .NET Framework just-in-time (JIT) compiler.

•The .NET Framework Ngen.exe (Native Image Generator). 4.4 Compilation by the JIT Compiler

JIT compilation converts MSIL to native code on demand at application run time, when the contents of an assembly are loaded and executed. Because the common language runtime

supplies a JIT compiler for each supported CPU architecture, developers can build a set of MSIL assemblies that can be JIT-compiled and run on different computers with different machine architectures. However, if your managed code calls platform-specific native APIs or a platform-

specific class library, it will run only on that operating system. JIT compilation takes into account the possibility that some code might never be called during

execution. Instead of using time and memory to convert all the MSIL in a PE file to native code, it converts the MSIL as needed during execution and stores the resulting native code in memory so that it is accessible for subsequent calls in the context of that process. The loader creates and

attaches a stub to each method in a type when the type is loaded and initialized. When a method is called for the first time, the stub passes control to the JIT compiler, which converts the MSIL for that method into native code and modifies the stub to point directly to the generated native code.

Therefore, subsequent calls to the JIT-compiled method go directly to the native code. Install-Time Code Generation Using NGen.exe

Because the JIT compiler converts an assembly's MSIL to native code when individual methods defined in that assembly are called, it affects performance adversely at run time. In most cases, that diminished performance is acceptable. More importantly, the code generated by the JIT

compiler is bound to the process that triggered the compilation. It cannot be shared across multiple processes. To allow the generated code to be shared across multiple invocations of an application or across multiple processes that share a set of assemblies, the common language

runtime supports an ahead-of-time compilation mode. This ahead-of-time compilation mode uses the Ngen.exe (Native Image Generator) to convert MSIL assemblies to native code much like the JIT compiler does. However, the operation of Ngen.exe differs from that of the JIT compiler in

three ways: •It performs the conversion from MSIL to native code before running the application instead of

while the application is running. •It compiles an entire assembly at a time, instead of one method at a time.

•It persists the generated code in the Native Image Cache as a file on disk.



4.5 Summary of Managed Code Execution Process

The process of compiling and executing managed code is given below: -

1. When you compile a program developed in a language that targets the CLR, instead of compiling the source code into machine-level code, the compiler translates it into Microsoft Intermediate Language (MSIL) or Intermediate language (IL). This ensures

language interoperability. 2. In addition to translating the code into IL, the compiler also produces metadata about the

program during the process of compilation. Metadata contains the description of the

program, such as classes and interfaces, the dependencies and the versions of the components used in the program.

3. The IL and the metadata are linked in assembly.

4. The compiler creates the .EXE or .DLL file. 5. When you execute the .EXE or .DLL file, the code (converted to IL) and all the other

relevant information from the base class library is sent to the class loader. The class

loader loads the code in the memory. 6. Before the code can be executed, the .NET framework needs to convert the IL into native

or CPU-specific code. The Just-in-time (JIT) compiler translates the code from IL to

managed native code. The CLR supplies a JIT compiler for each supported CPU architecture. During the process of compilation, the JIT compiler compiles only the code that is required during execution instead of compiling the complete IL code. When an

uncompiled method is invoked during execution, the JIT compiler converts the IL for that method into native code. This process saves the time and memory required to convert the complete IL into native code.

7. During JIT compilation, the code is also checked for type safety. Type safety ensures that objects are always accessed in a compatible way. Therefore, if you try to pass an 8-byte value to a method that accepts a 4-byte value as a parameter, the CLR will detect and

trap such an attempt. Type safety also ensures that objects are safely isolated from each other and are therefore safe from any malicious corruption.

8. After translating the IL into native code, the converted code is sent to the .NET runtime

manager. 9. The .NET runtime manager executes the code. While executing the code, a security

check is performed to ensure that the code has the appropriate permissions for

accessing the available resources. Common Language Infrastructure (CLI)

The Common Language Infrastructure (CLI) is an open specification developed by Microsoft that describes the executable code and runtime environment that allows multiple high-level languages

to be used on different computer platforms without being rewritten for specific architectures. The common language Infrastructure (CLI) is a theoretical model of a development platform that

provides a device and language independent way to express data and behavior of applications. The CLI specification describes the following four aspects: -

The Common Type System (CTS)

The language interoperability and .NET Class Framework are not possible without all the language sharing the same data type. CTS is an important part of the runtime support for cross-language integration. The CTS performs the following functions:

Establishes a framework that enables cross-language integration, type safety and high performance code execution.



Provides an object-oriented model that supports the complete implementation of many programming languages.

The CTS supports two general categories of types: -

1. Value Types Value types directly contain their data, and instances of value types are either allocated on the

stack or allocated inline in a structure. Value types can be built-in, user-defined or enumerations types.

2. Reference Types Reference types store a reference to the value’s memory address, and are allocated on the heap.

Reference types can be self-describing types, pointers type or interface types. The type of a reference type can be determined from values of self-describing types. Self-describing types are further split into arrays and class types are user-defined classes, boxed value types, and

delegates. A set of data types and operations that are shared by all CTS-compliant programming

languages.

Metadata

Information about program structure is language-agnostic, so that it can be referenced between languages and tools, making it easy to work with code written in a language you are not using.

Common Language Specification (CLS)

A set of base rules to which any language targeting the CLI should conform in order to interoperate with other CLS-compliant languages. The CLS rules define a subset of the Common Type System.

Virtual Execution System (VES)

The VES loads and executes CLI-compatible programs, using the metadata to combine separately generated pieces of code at runtime.

The Common Language Runtime The CLR is one of the most essential components of the .NET framework. The CLR or the

runtime provides functionality such as exception handling, security, debugging, and versioning support to any language that targets it. The CLR can execute programs written any language. You can use the compilers to write the code that runs in the managed execution environment

provided by the CLR. The code that is developed with a language compiler that targets the CLR is managed code. On the other hand, the code that is developed without considering the conventions and requirements of the common language run time is called unmanaged code.

CLR activates objects, performs security checks, lays them out in memory, executes them and garbage collects these objects as well.

The CLR is a runtime engine that loads required classes, performs just in time compilations, and enforces security checks and a bunch of other runtime functions.



The CLR executables are either exe or DLL files that consist mostly of metadata and code. These executables must adhere to a file format called the Portable Executable (PE) file format.

Features Provided by CLR

Some of the features provided by the CLR are as follows: -

Automatic Memory Management: The CLR provides the garbage collection feature for

managing the lifetime of an object. This process relieves a programmer of the task of manual memory management by deallocating the blocks of memory associated with objects that are no longer being used. The objects whose lifetime is managed by the

garbage collection process are called managed data.

Standard Type System: The CLR implements a formal specification called Common Type System (CTS). The CTS is an important part of the support provided by the CLR for

cross-language integration because it provides a type system that is common across all programming languages. It also defines the rules that ensure that objects written in different languages can interact with each other.

Language Interoperability: Language interoperability is the ability of an application to interact with another application written in a different programming language. Language

interoperability helps maximize code reuse. For example, you can write a class in Visual Basic and inherit it in a code written in Visual C++.

Platform Independence: When you compile a program developed in language that targets the CLR, the compiler translates the code into an intermediate language. This language is CPU-independent. This means that the code can be executed from any platform that

supports the .NET CLR.

Security Management The traditional operating system security model provides permissions to access resources, such as memory and data, based on user accounts. In

.NET platform security is achieved through the Code Access Security (CAS) model. The CAS model specifies what the code can access instead of specifying who can access resources.

Type Safety: This feature ensures that objects are always accessed in compatible ways. Therefore the CLR will prohibit a code from assigning a 10-byte value to an object that

occupies 8 bytes. Advantages of the .NET Framework

Consistent programming model

Multi-platform applications

Multi-Language integration

Automatic Resource Management

Ease of deployment



OOPS & C# The skeleton of object - oriented programming is of course the concepts of class. The C# on

OOPS explains classes and their importance in implementation of object oriented principles. Any language can be called object oriented if it has data and method that use data

encapsulated in items named objects. An object oriented programming method has many advantages; some of them are flexibility and code reusability.

Key Concepts of Object Orientation

Abstraction

Encapsulation

Inheritance

Polymorphism

Abstraction is the ability to generalize an object as a data type that has a specific set of

characteristics and is able to perform a set of actions.

Object-oriented languages provide abstraction via classes. Classes define the properties and methods of an object type.

Examples: You can create an abstraction of a dog with characteristics, such as color, height, and weight,

and actions such as run and bite. The characteristics are called properties, and the actions are called methods. A Recordset object is an abstract representation of a set of data.

Classes are blueprints for Object. Objects are instance of classes.

Object References When we work with an object we are using a reference to that object. On the other hand, when

we are working with simple data types such as Integer, we are working with the actual value rather than a reference.

When we create a new object using the New keyword, we store a reference to that object in a variable. For instance:

Draw MyDraw = new Draw; This code creates a new instance of Draw. We gain access to this new object via the MyDraw

variable. This variable holds a reference to the object. Now we have a second variable, which also has a reference to that same object. We can use

either variable interchangeably, since they both reference the exact same object. The thing we need to remember is that the variable we have is not the object itself but, rather, is just a reference or pointer to the object itself.

Early binding means that our code directly interacts with the object, by directly calling its methods. Since the compiler knows the object's data type ahead of time, it can directly compile

code to invoke the methods on the object. Early binding also allows the IDE to use IntelliSense to aid our development efforts; it allows the compiler to ensure that we are referencing methods that do exist and that we are providing the proper parameter values.



Late binding means that our code interacts with an object dynamically at run-time. This provides a great deal of flexibility since our code literally doesn't care what type of object it is interacting

with as long as the object supports the methods we want to call. Because the type of the object isn't known by the IDE or compiler, neither IntelliSense nor compile-time syntax checking is possible but we get unprecedented flexibility in exchange.

If we enable strict type checking by using Option Strict On at the top of our code modules, then the IDE and compiler will enforce early binding behavior. By default, Option Strict is turned off and

so we have easy access to the use of late binding within our code.

Access Modifiers

Access Modifiers are keywords used to specify the declared accessibility of a member of a type.

Public is visible to everyone. A public member can be accessed using an instance of a class, by

a class's internal code, and by any descendants of a class.

Private is hidden and usable only by the class itself. No code using a class instance can access

a private member directly and neither can a descendant class.

Protected members are similar to private ones in that they are accessible only by the containing

class. However, protected members also may be used by a descendant class. So members that are likely to be needed by a descendant class should be marked protected.



Internal/Friend is public to the entire application but private to any outside applications. Internal

is useful when you want to allow a class to be used by other applications but reserve special

functionality for the application that contains the class. Internal is used by C# and Friend by VB .NET.

Protected Internal may be accessed only by a descendant class that's contained in the same

application as its base class. You use protected internal in situations where you want to deny

access to parts of a class functionality to any descendant classes found in other applications.



Composition of an OBJECT We use an interface to get access to an object's data and behavior. The object's data and behaviors are contained within the object, so a client application can treat the object like a black

box accessible only through its interface. This is a key object-oriented concept called Encapsulation. The idea is that any programs that make use of this object won't have direct access to the behaviors or data-but rather those programs must make use of our object's

interface. There are three main parts of Object:

1. Interface 2. Implementation or Behavior

3. Member or Instance variables

Interface The interface is defined as a set of methods (Sub and Function routines), properties (Property routines), events, and fields (variables or attributes) that are declared Public in scope.

Implementation or Behavior The code inside of a method is called the implementation. Sometimes it is also called behavior since it is this code that actually makes the object do useful work.

Client applications can use our object even if we change the implementation-as long as we don't change the interface. As long as our method name and its parameter list and return data type remain unchanged, we can change the implementation all we want .

So Method Signature depends on:

Method name



Data types of parameters

Either Parameter is passed ByVal or ByRef.

Return type of method

It is important to keep in mind that encapsulation is a syntactic tool-it allows our code to continue to run without change. However, it is not semantic-meaning that, just because our code continues

to run, doesn't mean it continues to do what we actually wanted it to do.

Member or Instance Variables The third key part of an object is its data, or state. Every instance of a class is absolutely identical in terms of its interface and its implementation-the only thing that can vary at all is the data

contained within that particular object. Member variables are those declared so that they are available to all code within our class.

Typically member variables are Private in scope-available only to the code in our class itself. They are also sometimes referred to as instance variables or as attributes. The .NET Framework also refers to them as fields.

We shouldn't confuse instance variables with properties. A Property is a type of method that is geared around retrieving and setting values, while an instance variable is a variable within the class that may hold the value exposed by a Property.

Interface looks like a class, but has no implementation.

The only thing it contains is definitions of events, indexers, methods and/or properties. The reason interfaces only provide definitions is because they are inherited by classes and structs, which must provide an implementation for each interface member defined.

Defining an Interface: MyInterface.cs

interface IMyInterface { void MethodToImplement();

} Above listing shows defines an interface named IMyInterface. All the methods of Interface are public by default and no access modifiers (like private, public) are

allowed with any method of Interface. Using an Interface: InterfaceImplementer.cs

class InterfaceImplementer : IMyInterface {

public void MethodToImplement() { Console.WriteLine("MethodToImplement() called.");

} } The InterfaceImplementer class in above listing implements the IMyInterface interface. Indicating

that a class inherits an interface is the same as inheriting a class. In this case, the following syntax is used:

class InterfaceImplementer : IMyInterface



Note that this class inherits the IMyInterface interface; it must implement its all members. While

implementing interface methods all those needs to be declared public only. It does this by implementing the MethodToImplement() method. Notice that this method implementation has the exact same signature, parameters and method name, as defined in the IMyInterface interface.

Any difference will cause a compiler error.

Inheritance is the idea that one class, called a subclass, can be based on another class,

called a base class. Inheritance provides a mechanism for creating hierarchies of objects. Inheritance is an important object-oriented concept. It allows you to build a hierarchy of related

classes, and to reuse functionality defined in existing classes. Inheritance is the ability to apply another class's interface and code to your own class.

Normal base classes may be instantiated themselves, or inherited. Derived classes can inherit base class members marked with protected or greater access. The derived class is specialized to

provide more functionality, in addition to what its base class provides. Inheriting base class members in derived class is not mandatory.

C# supports two types of Inheritance mechanisms: - 1) Implementation Inheritance

2) Interface Inheritance

What is Implementation Inheritance? - When a class (type) is derived from another class(type) such that it inherits all the members of the base type it is Implementation Inheritance

What is Interface Inheritance?

- When a type (class or a struct) inherits only the signatures of the functions from another type it is Interface Inheritance

In general, Classes can be derived from another class, hence support Implementation inheritance At the same time Classes can also be derived from one or more interfaces Hence they support Interface inheritance Structs can derive from one more interface, hence support Interface

Inheritance Structs cannot be derived from another class they are always derived from SystemValueType

Types of Inheritance

1. Single Inheritance 2. Multilevel Inheritance

3. Multiple Inheritance (Implementation is possible through Interface)

4. Hierarchical Inheritance



Example: -

Single Inheritance: - Multilevel Inheritance: - Hierarchical Inheritance: - public class A public class A public class A { } { } { } public class B : A public class B : A public class B : A { } { } { } public class C : B public class C : A

Multiple Inheritance : - { } { } public class A public class D : A { } { } public class B { } public class C : A, B

{ }

Polymorphism

Polymorphism is the ability to define a method or property in a set of derived classes with matching method signatures but provide different implementations and then distinguish the

objects' matching interface from one another at runtime when you call the method on the base class. It is a feature to use one name in many forms. It can be achieved in following ways: -

Method Overloading

Method Overriding

Method Hiding

Class B Class B

Single Inheritance

Class A

Class D Class C

Class A

Hierarchical Inheritance

Class A

Class B

Class C

Class A Class B

Class C

Multiple Inheritance Multilevel Inheritance



Method overriding and hiding makes use of the following three method keywords –

1. new 2. virtual 3. override

1. When a derived class inherits from a base class, it gains all the methods, fields, properties and

events of the base class. To change the data and behavior of a base class, you have two choices: you can replace the base member with a new derived member, or you can override a

virtual base member. Replacing a member of a base class with a new derived member requires the new keyword. If a

base class defines a method, field, or property, the new keyword is used to create a new definition of that method, field, or property on a derived class. The new keyword is placed before the return type of a class member that is being replaced. For example:

public class BaseClass {

public void DoWork() { } public int WorkField; public int WorkProperty

{ get { return 0; } }

} public class DerivedClass : BaseClass {

public new void DoWork() { } public new int WorkField; public new int WorkProperty

{ get { return 0; } }

} DerivedClass B = new DerivedClass();

B.DoWork(); // Calls the new method. BaseClass A = (BaseClass)B;

A.DoWork(); // Calls the old method. 2,3. In order for an instance of a derived class to completely take over a class member from a

base class, the base class has to declare that member as virtual. This is accomplished by adding

the virtual keyword before the return type of the member. A derived class then has the option of using the override keyword, instead of new, to replace the base class implementation with its own. For example:

public class BaseClass {

public virtual void DoWork() { } public virtual int WorkProperty {

get { return 0; } } }



public class DerivedClass : BaseClass {

public override void DoWork() { } public override int WorkProperty {

get { return 0; } } }

DerivedClass B = new DerivedClass(); B.DoWork(); // Calls the new method.

BaseClass A = (BaseClass)B; A.DoWork(); // Also calls the new method.

Remarks about Virtual

When a virtual method is invoked, the run-time type of the object is checked for an overriding member. The overriding member in the most derived class is called, whic h

might be the original member, if no derived class has overridden the member.

By default, methods are non-virtual. You cannot override a non-virtual method.

You cannot use the virtual modifier with the static, abstract, private or override modifiers.

Virtual properties behave like abstract methods, except for the differences in declaration and invocation syntax.

It is an error to use the virtual modifier on a static property.

A virtual inherited property can be overridden in a derived class by including a property declaration that uses the override modifier.

Remarks about Override

The override modifier is required to extend or modify the abstract or virtual implementation of an inherited method, property, indexer, or event.

An override method provides a new implementation of a member inherited from a base class. The method overridden by an override declaration is known as the overridden base

method. The overridden base method must have the same signature as the override method.

You cannot override a non-virtual or static method. The overridden base method must be virtual, abstract, or override.

An override declaration cannot change the accessibility of the virtual method. Both the

override method and the virtual method must have the same access level modifier.

You cannot use the modifiers new, static, virtual, or abstract to modify an override

method.

An overriding property declaration must specify the exact same access modifier, type, and name as the inherited property, and the overridden property must be virtual, abstract,

or override.



Class and Objects Classes

A class is a construct that enables you to create your own custom types by grouping together variables of other types, methods and events. A class is like a blueprint. It defines the data and

behavior of a type. If the class is not declared as static, client code can use it by creating objects or instances which are assigned to a variable. The variable remains in memory until all references to it go out of scope. At that time, the CLR marks it as eligible for garbage collection. If the class

is declared as static, then only one copy exists in memory and client code can only access it through the class itself, not an instance variable.

Declaring Class public class Customer

{ //Fields, properties, methods and events go here... }

The class keyword is preceded by the access level. Because public is used in this case, anyone can create objects from this class. The name of the class follows the class keyword.

Objects

An object is basically a block of memory that has been allocated and configured according to the blueprint. A program may create many objects of the same class. Objects are also called instances, and they can be stored in either a named variable or in an array or collection.

Creating Objects A class and an object are different things. A class defines a type of object, but it is not an object

itself. An object is a concrete entity based on a class, and is sometimes referred to as an instance of a class.

Objects can be created by using the new keyword followed by the name of the class that the object will be based on, like this:

Customer object1 = new Customer(); When an instance of a class is created, a reference to the object is passed back to the

programmer. In the previous example, object1 is a reference to an object that is based on Customer.

Class Modifiers A class-declaration can optionally include a sequence of class modifiers:

class-modifiers: class-modifier class-modifiers class-modifier

class-modifier: new, public, protected, internal, private, abstract, sealed



The new modifier is permitted on nested classes. The new modifier can be used to modify a

nested type if the nested type is hiding another type.

The public, protected, internal, and private modifiers control the accessibility of the class.

Depending on the context in which the class declaration occurs, some of these modifiers may not

be permitted The abstract modifier is used to indicate that a class is incomplete and that it is intended to be

used only as a base class. An abstract class differs from a non-abstract class in the following

ways:

An abstract class cannot be instantiated directly, and it is a compile-time error to use the new operator on an abstract class. While it is possible to have variables and values

whose compile-time types are abstract, such variables and values will necessarily either be null or contain references to instances of non-abstract classes derived from the abstract types.

An abstract class is permitted (but not required) to contain abstract methods and members.

An abstract class cannot be sealed.

Features of Abstract Methods:

An abstract method is implicitly a virtual method.

Abstract method declarations are only permitted in abstract classes.

Because an abstract method declaration provides no actual implementation, there is no method body; the method declaration simply ends with a semicolon and there are no braces ({ }) following the signature. For example:

Copypublic abstract void MyMethod();

The implementation is provided by an overriding method, which is a member of a non-abstract class.

It is an error to use the static or virtual modifiers in an abstract method declaration.

Abstract properties behave like abstract methods, except for the differences in declaration and invocation syntax.

It is an error to use the abstract modifier on a static property.

An abstract inherited property can be overridden in a derived class by including a property declaration that uses the override modifier.

An abstract class must provide implementation for all interface members. Example: -

// abstract_keyword.cs // Abstract Classes

using System; abstract class MyBaseC // Abstract class {

protected int x = 100; protected int y = 150; public abstract void MyMethod(); // Abstract method



public abstract int GetX // Abstract property {

get; }

public abstract int GetY // Abstract property { get;

} }

class MyDerivedC: MyBaseC { public override void MyMethod()

{ x++; y++;

} public override int GetX // overriding property

{ get {

return x+10; } }

public override int GetY // overriding property {

get { return y+10;

} }

public static void Main() { MyDerivedC mC = new MyDerivedC();

mC.MyMethod(); Console.WriteLine("x = {0}, y = {1}", mC.GetX, mC.GetY); }

} The sealed modifier is used to prevent derivation from a class. A compile-time error occurs if a

sealed class is specified as the base class of another class.

A sealed class cannot also be an abstract class. The sealed modifier is primarily used to prevent unintended derivation, but it also enables certain

run-time optimizations. In particular, because a sealed class is known to never have any derived classes, it is possible to transform virtual function member invocations on sealed class instances into non-virtual invocations.

Example: use of Sealed modifier

// cs_sealed_keyword.cs



// Sealed classes using System;

sealed class MyClass { public int x;

public int y; }

class MainClass { public static void Main()

{ MyClass mC = new MyClass(); mC.x = 110;

mC.y = 150; Console.WriteLine("x = {0}, y = {1}", mC.x, mC.y); }

} Output: x=110, y=150

Constructors

Whenever a class or struct is created, its constructor is called. A class or struct may have multiple constructors that take different arguments.

Constructors allow the programmer to set default values, limit instantiation, and write code that is flexible and easy to read.

Constructor is used to initialize an object (instance) of a class.

Constructor is a like a method without any return type.

Constructor has same name as class name.

Constructor follows the access scope (Can be private, protected, public, Internal and

external).

Constructor can be overloaded. Constructors generally following types:

Default Constructor

Parameterized constructor

Private Constructor

Static Constructor

Copy Constructor

Default Constructor A constructor that takes no parameters is called a default constructor.

When a class is initiated default constructor is called which provides default values to different data members of the class.

You need not to define default constructor it is implicitly defined.



Example: -

class Program

{

class C1

{

int a, b;

public C1()

{

this.a = 10;

this.b = 20;

}

public void display()

{

Console.WriteLine("Value of a: {0}", a);

Console.WriteLine("Value of b: {0}", b);

}

}

static void Main(string[] args)

{

C1 ob1 = new C1();

ob1.display();

Console.ReadLine();

}

}

Output: - Value of a: 10 Value of b: 20

Parameterized constructor Constructor that accepts arguments is known as parameterized constructor. There may be

situations, where it is necessary to initialize various data members of different objects with different values when they are created. Parameterized constructors help in doing that task.

class Program

{

class C1

{

int a, b;

public C1(int x, int y)

{

this.a = x;

this.b = y;

}


{





}

}


{ // Here when you create instance of the class // parameterized constructor will be called

C1 ob1 = new C1(10,20);

ob1.display();

Console.ReadLine();

}

}

Output: - Value of a: 10

Value of b: 20 Private Constructor

Private constructors are used to restrict the instantiation of object using 'new' operator. A private constructor is a special instance constructor. It is commonly used in classes that contain static

members only.

If you don't want the class to be inherited we declare its constructor private.

We can't initialize the class outside the class or the instance of class can't be created outside if its constructor is declared private.

We have to take help of nested class (Inner Class) or static method to initialize a class having private constructor.

Example: - class Program

{

class C1

{

int a, b;

public C1(int x, int y)

{

this.a = x;

this.b = y;

}

public static C1 create_instance()

{ return new C1(12, 20); }


{



int z = a + b;

Console.WriteLine(z);

}

}


{ // Here the class is initiated using a static method of the class than only you can use private constructor



C1 ob1 = C1.create_instance();

ob1.display();

Console.ReadLine();

}

}

Static Constructors

C# supports two types of constructor, a class constructor static constructor and an instance constructor (non-static constructor).

Static constructors might be convenient, but they are slow. The runtime is not smart enough to optimize them in the same way it can optimize inline assignments. Non-static constructors are

inline and are faster. Static constructors are used to initializing class static data members.

Point to be remembered while creating static constructor:

1. There can be only one static constructor in the class. 2. The static constructor should be without parameters. 3. It can only access the static members of the class. 4. There should be no access modifier in static constructor definition.

Static members are preloaded in the memory. While instance members are post loaded into memory.

Static methods can only use static data members. Example:

class Program

{

public class test

{

static string name;

static int age;

static test()

{

Console.WriteLine("Using static constructor to initialize

static data members");

name = "John Sena";

age = 23;

}

public static void display()

{

Console.WriteLine("Using static function");

Console.WriteLine(name);

Console.WriteLine(age);

}

}


{

test.display();

Console.ReadLine();

}}



Output: Using static constructor to initialize static data members

Using static function John Sena 23

Copy Constructor

If you create a new object and want to copy the values from an existing object, you use copy constructor. This constructor takes a single argument: a reference to the object to be copied.

Example:

class Program

{

class c1

{

int a, b;

public c1(int x, int y)

{

this.a = x;

this.b = y;

}

// Copy construtor

public c1(c1 a)

{

this.a = a.a;

this.b = a.b;

}


{

int z = a + b;

Console.WriteLine(z);

}

}


{

c1 ob1 = new c1(10, 20);

ob1.display();

// Here we are using copy constructor. Copy

constructor is

using the values already defined with ob1

c1 ob2 = new c1(ob1);

ob2.display();

Console.ReadLine();

}

}

Output: 30 30



Destructors

The .NET framework has an in built mechanism called Garbage Collection to de-allocate memory occupied by the un-used objects. The destructor implements the statements to be executed during the garbage collection process. A destructor is a function with the same name as the name

of the class but starting with the character ~. Example:

class Complex {

public Complex() { // constructor

} ~Complex() {

// Destructor } }

Remember that a destructor can't have any modifiers like private, public etc. If we declare a destructor with a modifier, the compiler will show an error.

Also destructor will come in only one form, without any arguments.

There is no parameterized destructor in C#. Destructors are invoked automatically and can't be invoked explicitly. An object becomes eligible

for garbage collection, when it is no longer used by the active part of the program. Execution of destructor may occur at any time after the instance or object becomes eligible for destruction.

Operator Overloading

Operator overloading permits user-defined operator implementations to be specified for operations where one or both of the operands are of a user-defined class or struct type.

In another way, Operator overloading is a concept in which operator can define to work with the user defined data types such as structs and classes in the same way as the pre-defined data types.

There are many operators which can not be overloaded, which are listed below: -

Conditional Operator &&, || Compound Assignment +=, -=, *=, /=, %=

Other Operators [], ( ), =, ?:, ->, new, sizeof, typesof.



public class Item

{

public int i;

public Item(int j)

{ i = j; }

public static Item operator +(Item x, Item y)

{

Console.WriteLine("OPerator +" + x.i + "" + y.i);

Item z = new Item(x.i + y.i);

return z;

}

}

class Program

{


{

Item a = new Item(10);

Item b = new Item(5);

Item c;

c = a + b;

Console.WriteLine(c.i);

Console.Read();

}

}

Output: Operator + 10 5 15

In C#, a special function called operator function is used for overloading purpose.

These special function or method must be public and static.

They can take only value arguments.

The ref and out parameters are not allowed as arguments to operator functions.

The general form of an operator function is as follows.

public static return_type operator op (argument list) Where the op is the operator to be overloaded and operator is the required keyword.

Example: Overloading of Unary operator class Complex

{

private int x;

private int y;

public Complex()

{}

public Complex(int i, int j)

{



x = i;

y = j;

}

public void ShowXY()

{

Console.WriteLine("{0}\t{1}",x,y);

}

public static Complex operator -(Complex c) //PASSING OBJECT

{

Complex temp = new Complex();

temp.x = -c.x;

temp.y = -c.y;

return temp;

}

}

class Program

{


{

Complex c1 = new Complex(10, 20);

c1.ShowXY(); // displays 10 & 20

Complex c2 = new Complex();

c2.ShowXY(); // displays 0 & 0

c2 = -c1; //overloading unary operator

c2.ShowXY(); // diapls -10 & -20

Console.Read();

}

} Output: 10 20

0 0 -10 -20

Namespace:

Namespaces are C# program elements designed to help you organize your programs. They also

provide assistance in avoiding name clashes between two sets of code. In Microsoft .Net, Namespace is like containers of objects. They may contain unions, classes,

structures, interfaces, enumerators and delegates. Main goal of using namespace in .Net is for creating a hierarchical organization of program. In this case, you need not to worry about the naming conflicts of classes, functions, variables etc., inside a project.

In Microsoft .Net, every program is created with a default namespace. This default namespace is called as global namespace. But the program itself can declare any number of namespaces, each

of them with a unique name. The advantage is that every namespace can contain any number of classes, functions, variables and also namespaces etc., whose names are unique only inside the



namespace. The members with the same name can be created in some other namespace without any compiler complaints from Microsoft .Net.

To declare namespace C# .Net has a reserved keyword namespace. If a new project is created in

Visual Studio .NET it automatically adds some global namespaces. These namespaces can be different in different projects. But each of them should be placed under the base namespace System. The names space must be added and used through the using operator, if used in a

different project. A namespace has the following properties:

They organize large code projects.

They are delimited with the . operator.

The using directive means you do not need to specify the name of the namespace for every class.

The global namespace is the "root" namespace: global::system will always refer to the .NET Framework namespace System.

Now have a look at the example of declaring some namespace:

namespace SampleNamespace {

class SampleClass{} interface SampleInterface{} struct SampleStruct{}

enum SampleEnum{a,b} delegate void SampleDelegate(int i); namespace SampleNamespace.Nested

{ class SampleClass2{} }

} Within a namespace, you can declare one or more of the following types:

another namespace

class

interface

struct

enum

delegate

Namespaces implicitly have public access and this is not modifiable. It is possible to define a namespace in two or more declarations. For example, the following

example defines two classes as part of the MyCompany namespace: namespace MyCompany.Proj1

{ class MyClass {

} }



namespace MyCompany.Proj1

{ class MyClass1 {

} }

Example: The following example shows how to call a static method in a nested namespace: using System; namespace SomeNameSpace

{ public class MyClass {

static void Main() { Nested.NestedNameSpaceClass.SayHello();

} }

// a nested namespace namespace Nested {

public class NestedNameSpaceClass { public static void SayHello()

{ Console.WriteLine("Hello"); }

} } }

Output Hello

Example: Calling Nested Namespace Members // Namespace Declaration using System;

namespace Ex_nestedNamespace {

namespace tutorial { class example

{ public static void MyPrint1() {

Console.WriteLine("First Example of calling another namespace member."); } }

}



namespace Ex_NameSpace {

class Program { static void Main(string[] args)

{ tutorial.example.MyPrint1(); tutorial.example1.MyPrint2();

Console.Read(); } }

} } namespace Ex_nestedNamespace.tutorial

{ class example1 {

public static void MyPrint2() { Console.WriteLine("Second Example of calling another namespace member.");

} } }

Output:

First Example of calling another namespace member. Second Example of calling another namespace member.

Interface

An Interface is a reference type and it contains only abstract members. Interface's members can be Events, Methods, Properties and Indexers. But the interface contains only declaration for i ts members. Any implementation must be placed in class that realizes them. The interface can not

contain constants, data fields, constructors, destructors and static members. All the member declarations inside interface are implicitly public and they cannot include any access modifiers.

An interface has the following properties:

An interface is like an abstract base class: any non-abstract type that implements the

interface must implement all its members.

An interface cannot be instantiated directly.

Interfaces can contain events, indexers, methods, and properties.

Interfaces contain no implementation of methods.

Classes and structs can implement more than one interface.

An interface itself can inherit from multiple interfaces.

interface IPoint

{



int x { get; set; }

int y { get; set; }

} namespace Ex_Interface {

class MyPoint:IPoint { private int myX;

private int myY; public MyPoint(int x, int y) {

myX= x; myY=y; }

public int x { get

{ return myX; }

set { myX=value;

} } public int y

{ get {

return myY; } set

{ myY=value; }

} }

class Program { private static void PrintPoint(IPoint P)

{ Console.WriteLine("x={0}, y={1}",P.x,P.y); }

static void Main(string[] args) {

MyPoint P = new MyPoint(2, 3); Console.Write("My Point::"); PrintPoint(P);

Console.Read(); } }



}

Output: My Point::x=2, y=3

Another Example of Interface by Casting Interface methods:

interface add { int sum();} interface Multiply

{ int mul();} class Calculate : add, Multiply {

int a, b; public Calculate(int x, int y) {

a = x; b = y; }

public int sum() { return (a + b);} public int mul()

{ return a * b; } } namespace Ex_MultipleInterface {


{ Calculate cal = new Calculate(5, 10); add A = (add)cal;

Console.WriteLine("Sum::" + A.sum()); Multiply M = (Multiply)cal; Console.WriteLine("Multiplication::" + M.mul());

Console.Read(); } }

} Output:

Sum::15 Multiplication::50



Delegates

In .NET, you use delegates to call event procedure. Delegates are objects that you use to call the methods of other objects. Delegates are said to be object-oriented function pointers since they

allow a function to be invoked indirectly by using a reference to the function. However, unlike function pointers, the delegates in .NET are reference types, based on the class

System.Delegate. In addition, delegates in .NET can reference both shared and instance methods.

In another way, a delegate can be defined as a type safe function pointer. You use delegates

to call the methods of other objects. They are object-oriented function pointers since they allow a function to be invoked indirectly by using a reference to the function.

Where are Delegates used?

The most common example of using delegates is in events.

You define a method that contains code for performing various tasks when an event (such as a mouse click) takes place.

This method needs to be invoked by the runtime when the event occurs. Hence this method, that you defined, is passed as a parameter to a delegate.

Starting Threads/Parallel Processing:

You defined several methods and you wish to execute them simultaneously and in parallel to

whatever else the application is doing. This can be achieved by starting new threads. To start a new thread for your method you pass your method details to a delegate.

Generic Classes: Delegates are also used for generic class libraries which have generic functionality defined. However the generic class may need to call certain functions defined by the end user implementing the generic class. This can be done by passing the user defined functions

to delegates.

Creating and Using Delegates:

Using delegates is a two step process-

..........1) Define the delegate to be used

..........2) Create one or more instances of the delegate

Syntax for defining a delegate:

delegate string reviewStatusofARegion();

to define a delegate we use a key word delegate followed by the method signature the delegate represents. In the above example string reviewStatusofARegion(); represents any method that returns a string and takes no parameters.

Syntax for creating an instance of the delegate:



reviewStatusofARegion = new reviewStatusofARegion(myClass.getEurope);

private string getEurope() { return “Doing Great in Europe”;

}

To create an instance of the delegate you call its constructor. The delegate constructor takes one

parameter which is the method name.

The method signature should exactly match the original definition of the delegate. If it does not

match the compiler would raise an Error.

C# provides support for Delegates through the class called Delegate in the System

namespace. Delegates are of two types.

Single-cast delegates

Multi-cast delegates

A Single-cast delegate is one that can refer to a single method whereas a Multi-cast

delegate can refer to and eventually fire off multiple methods that have the same signature.

The signature of a delegate type comprises are the following.

The name of the delegate

The arguments that the delegate would accept as parameters

The return type of the delegate

A delegate is either public or internal if no specifier is included in its signature. Further, you should instantiate a delegate prior to using the same.

The following is an example of how a delegate is declared. Listing 1: Declaring a delegate

public delegate void TestDelegate(string message);

The return type of the delegate shown in the above example is "void" and it accepts a string argument. Note that the keyword "delegate" identifies the above declaration as a delegate to a method. This delegate can refer to and eventually invoke a method that can accept a string

argument and has a return type of void, i.e., it does not return any value. Listing 2: Instantiating a delegate

TestDelegate t = new TestDelegate(Display);

Implementing Delegates in C# This section illustrates how we can implement and use delegates in C#.This section illustrate how we can implement and use delegates in C#.



Example 1: Single Cast Delegate

namespace Ex_Delegate { delegate int Operation(int x, int y); //declaration

class Metaphor { public static int Add(int a, int b)

{ return a + b; } public static int Sub(int a, int b) { return a - b; }

public static int Mul(int a, int b) { return a * b; } }


{ // Delegate instances Operation opr1 = new Operation(Metaphor.Add); Operation opr2 = new Operation(Metaphor.Sub);

Operation opr3 = new Operation(Metaphor.Mul); //invoking of delegates int ans1 = opr1(200, 100);

int ans2 = opr2(200, 100); int ans3 = opr3(20, 10); Console.WriteLine("\n Addition:" + ans1);

Console.WriteLine("\n Subtract:" + ans2); Console.WriteLine("\n Multiplication:" + ans3); Console.Read();

} }} Example 2: Single Cast Delegate

namespace Ex_SingleCastDelegate { //Declare the delegate

public delegate void TestDelegate(string message); class Program {

public static void Display(string message) {Console.WriteLine("The string entered is : " + message);}

static void Main(string[] args) { //Initiate the delegate

TestDelegate t = new TestDelegate(Display);

Console.WriteLine("Please enter a string::"); string message = Console.ReadLine(); t(message);

Console.ReadLine(); }}}

Multicast Delegate

A multi-cast delegate is basically a list of delegates or a list of methods with the same signature. A multi-cast delegate can call a collection of methods instead of only a single method.



Example: Multicast Delegate

namespace Ex_MulticastDelegate { public delegate void TestDelegate(); class Program { public static void Display1() { Console.WriteLine("This is first method"); } public static void Display2() { Console.WriteLine("This is second method"); } static void Main(string[] args) { TestDelegate t1 = new TestDelegate(Display1); TestDelegate t2 = new TestDelegate(Display2); t1 = t1 + t2; // Make t1 a multi-cast delegate t1(); //Invoke delegate Console.Read(); } } } In another way, You can also assign the references of multiple methods to a delegate and use it to invoke multiple methods. Such a delegate is called a multi-cast delegate as multiple method references are cast to it and then the delegate is used to invoke these methods.

What are Attributes?

An Attribute is a declarative tag which can be used to provide information to the compiler about the behaviour of the C# elements such as classes and assemblies. C# provides convenient technique that will handle tasks such as performing compile time

operations , changing the behaviour of a method at runtime or maybe even handle unmanaged code. C# Provides many Built-in Attributes.

Some Popular ones are

Obsolete

DllImport

Conditional

WebMethod

It is also possible to create new ones by extending the System.Attribute class. For example:

using System; [CLSCompliant(true)] Public class myClass

{ // class code } Web services also make use of attributes. The attribute [WebMethod] is used to specify that a

particular method is to be exposed as a web service.



Why Attributes ?

The reason attributes are necessary is because many of the services they provide would be very difficult to accomplish with normal code. You see, attributes add what is called metadata to your

programs. When your C# program is compiled, it creates a file called an assembly, which is normally an executable or DLL library. Assemblies are self-describing because they have metadata written to them when they are compiled. Via a process known as reflection, a program's

attributes can be retrieved from its assembly metadata. Attributes are classes that can be written in C# and used to decorate your code with declarative information. This is a very powerful concept because it means that you can extend your language by creating customized declarative

syntax with attributes. How it is used in C#?

Attributes are elements that allow you to add declarative information to your programs. This declarative information is used for various purposes during runtime and can be used at design

time by application development tools. For example, there are attributes such as DllImportAttribute that allow a program to communicate with the Win32 libraries. Another attribute, ObsoleteAttribute, causes a compile-time warning to appear, letting the developer know

that a method should no longer be used. When building Windows forms applications, there are several attributes that allow visual components to be drag-n-dropped onto a visual form builder and have their information appear in the properties grid. Attributes are also used extensively in

securing .NET assemblies, forcing calling code to be evaluated against pre-defined security constraints. These are just a few descriptions of how attributes are used in C# programs.

Predefined .NET

Attribute

Valid Targets Description

AttributeUsage Class Specifies the valid usage of another attribute class.

CLSCompliant All Indicates whether a program element is compliant with the Common Language

Specification (CLS).

DllImport Method Specifies the DLL location that contains the implementation of an external method.

MTAThread Method (Main) Indicates that the default threading model for an application is multithreaded apartment (MTA).

NonSerialized Field Applies to fields of a class flagged as

Serializable; specifies that these fields won’t be serialized.

Obsolete All except Assembly, Module, Parameter, and Return

Marks an element obsolete—in other words, it informs the user that the element will be

removed in future versions of the product.

ParamArray Parameter Allows a single parameter to be implicitly treated as a params (array) parameter.

Serializable Class, struct, enum, delegate Specifies that all public and private fields of this type can be serialized.

STAThread Method (Main) Indicates that the default threading model for an

application is STA.

ThreadStatic Field (static) Implements thread-local storage (TLS)—in other words, the given static field isn’t shared across multiple threads and each thread has its own

copy of the static field.



Predefined attributes

Example: Pre-defined attributes are used to store external information into metadata. For example, consider

the following piece of code:

public class testAttribute { [DllImport("sampleDLL.dll")] public static extern sampleFunction(int sampleNo, string sampleString ); public static void Main( ) { string strVar; sampleFunction(10, “Test Attribute”); } }

Using the example code above, you can import a method called sampleFunction from sampleDLL.dll and use it in your program as if it’s your own method. This is achieved using the pre-defined attribute “DllImport”.



Multi-Threading Multithreading forms a subset of multitasking. Instead of having switch between programs this

feature switches between different parts of the same program. For example when you are writing words in Ms-word then spell checking is going on background.

Thread - A thread (or "thread of execution") is a sort of context in which code is running. Any one thread follows program flow for wherever it is in the code, in the obvious way.

A thread is a unit of processing, and multitasking is the simultaneous execution of multiple threads. Multitasking comes in two flavors: cooperative and preemptive. Very early versions of Microsoft Windows supported cooperative multitasking, which meant that each thread was

responsible for relinquishing control to the processor so that it could process other threads. However, Microsoft Windows NT-and, later, Windows 95, Windows 98, and Windows 2000-

support the same preemptive multitasking that OS/2 does. With preemptive multitasking, the processor is responsible for giving each thread a certain amount of time in which to execute-a timeslice. The processor then switches among the different threads, giving each its timeslice, and

the programmer doesn't have to worry about how and when to relinquish control so that other threads can run. .NET will only work only on preemptive multitasking operating systems.

1. Starting Thread Object thread is obtained from System.Threading namespace. With the use object of this class we can create a new thread, delete, pause, and resume threads. Simple a new thread is created

by Thread class and started by Thread.Start(). eg. Thread th = new Thread (new ThreadStart (somedata)); th.Start();

2. Pausing Thread Some time the requirement to pause a thread for certain time of interval; you can attain the same by using Sleep (n) method. This method takes an integer value to determine how long a thread

should pause or Sleep. eg. th.Sleep(2000);

Note: To pause or sleep a thread for an in determine time, just call the sleep () method as: [make sure you have added System.Threading namespace] Thread.Sleep(TimeOut.Infinite).

To Resume or interrupt this call : Thread.Interrupt () method. 3. Suspending Thread

Of course, there is a Suspend () method which suspends the thread. It is suspended until a Resume () method called.

eg. if (th.ThreadState = = ThreadState.Running) th.Suspended();

4. Resuming Thread To Resume a suspended thread, there is a Resume () method, thread resumes if earlier

suspended if not so then there is no effect of Resume () method on the thread. eg. if (th.ThreadState = = ThreadState.Suspended)

th.Resume();



5. Killing Thread You can call Abort () method to kill a thread, before calling the same method, make sure thread is

alive. eg. if (th.IsAlive)

th.Abort(); Suspend and Resume in Threading

It is similar to sleep and Interrupt. Suspend allows you to block a thread until another thread calls Thread.Resume ().The difference between sleep and suspend is that the later does no immediately place a thread in the wait state. The thread does not suspend until the .Net runtime

determines that it is in a safe place to suspend it. Sleep will immediately place a thread in a wait state.

Important: You can change thread priority for that just supply : th.Priority = ThreadPriority.Highest. [th – Thread name]. Priority sets the sequence of thread in which they are running. You can set the

following priority to thread(s): 1. ThreadPriority.Highest

2. ThreadPriority.AboveNormal 3. ThreadPriority.Normal 4. ThreadPriority.BelowNormal

5. ThreadPriority.Lowest Code Example of Multithreading

using System.Threading;

namespace Ex_ThreadExample

{

class SimpleThread

{

private Thread thread1;

private Thread thread2;

private void Method1()

{

for (int i =0; i<10;i++)

{

Console.WriteLine ("i = " +i);

Thread.Sleep (400); // 200 miliseconds pause

}

}

private void Method2()

{

for (int i =0;i<10;i++)

{

Console.WriteLine ("i = " + 100 * i);

Thread.Sleep (100); // 100 miliseconds pause

}

}


{

SimpleThread app = new SimpleThread ();



app.thread1 = new Thread (new ThreadStart (app.Method1));

// thread start Delegate Method

app.thread2 = new Thread (new ThreadStart (app.Method2));

app.thread1.Start ();

app.thread2.Start ();

Console.WriteLine ();

Console.ReadLine();

}

}

}

-----------x----------------x--------------------------x-------------------------x----------------x---------------x----------

Exception Handling Overview of Exception Handling

Exceptions are error conditions that arise when the normal flow of a code path-that is, a series of method calls on the call stack-is impractical. Exception handling is an in built mechanism in .NET framework to detect and handle run time errors. The exceptions are anomalies that occur during

the execution of a program. They can be because of user, logic or system errors. If a user (programmer) do not provide a mechanism to handle these anomalies, the .NET run time environment provide a default mechanism, which terminates the program execution. C# provides

three keywords try, catch and finally to do exception handling. The try encloses the statements that might throw an exception whereas catch handles an exception if one exists. The finally can be used for doing any clean up process.

The general form try-catch-finally in C# is shown below:

try { // Statement which can cause an exception.

} catch(Type x) {

// Statements for handling the exception } finally

{ //Any cleanup code }

If any exception occurs inside the try block, the control transfers to the appropriate catch block and later to the finally block.

But in C#, both catch and finally blocks are optional. The try block can exist either with one or more catch blocks or a finally block or with both catch and finally blocks.

If there is no exception occurred inside the try block, the control directly transfers to finally block. We can say that the statements inside the finally block is executed always. Note that it is an error

to transfer control out of a finally block by using break, continue, return or goto. In C#, exceptions are nothing but objects of the type Exception. The Exception is the ultimate

base class for any exceptions in C#. The C# itself provides couple of standard exceptions. Or even the user can create their own exception classes, provided that this should inherit from either



Exception class or one of the standard derived classes of Exception class like DivideByZeroExcpetion ot ArgumentException etc.

The modified form of the above program with exception handling mechanism is as follows : -

//C#: Exception Handling using System; class MyClient

{ public static void Main() {

int x = 0; int div = 0; try { div = 100/x;

Console.WriteLine("Not executed line"); } catch(DivideByZeroException de)

{ Console.WriteLine("Exception occured"); } finally { Console.WriteLine("Finally Block"); }

Console.WriteLine("Result is {0}",div); } }

Multiple Catch Blocks

A try block can throw multiple exceptions, which can handle by using multiple catch blocks. Remember that more specialized catch block should come before a generalized one. Otherwise

the compiler will show a compilation error. //C#: Exception Handling: Multiple catch

using System; class MyClient {

public static void Main() { int x = 0;

int div = 0; try {

div = 100/x; Console.WriteLine("Not executed line");

}

catch(DivideByZeroException de) { Console.WriteLine("DivideByZeroException" ); } catch(Exception ee)

{ Console.WriteLine("Exception" ); } finally { Console.WriteLine("Finally Block"); }




Catching All Exception

By providing a catch block without a brackets or arguments, we can catch all exceptions occurred inside a try block. Even we can use a catch block with an Exception type parameter to catch all exceptions happened inside the try block since in C#, all exceptions are directly or indirectly

inherited from the Exception class. //C#: Exception Handling: Handling all exceptions

using System; class MyClient {

public static void Main() { int x = 0;

int div = 0; try { div = 100/x;

Console.WriteLine("Not executed line"); } catch

{ Console.WriteLine("oException" );} Console.WriteLine("Result is {0}",div); }

}

The following program handles all exception with Exception object.

//C#: Exception Handling: Handling all exceptions using System; class MyClient


int x = 0; int div = 0;

try

{ div = 100/x; Console.WriteLine("Not executed line");

} catch(Exception e) { Console.WriteLine("oException" );}


Throwing an Exception

In C#, it is possible to throw an exception programmatically. The 'throw' keyword is used for this purpose. The general form of throwing an exception is as follows.

throw exception_obj; For example the following statement throws an ArgumentException explicitly.



throw new ArgumentException("Exception");

Example

//C#: Exception Handling: using System; class MyClient


try { throw new DivideByZeroException("Invalid Division");} catch(DivideByZeroException e)

{ Console.WriteLine("Exception" ); } Console.WriteLine("LAST STATEMENT"); }

} Standard Exceptions

There are two types of exceptions: exceptions generated by an executing program and exceptions generated by the common language runtime. System.Exception is the base class for

all exceptions in C#. Several exception classes inherit from this class including ApplicationException and SystemException. These two classes form the basis for most other runtime exceptions. Other exceptions that derive directly from System.Exception include

IOException, WebException etc. The common language runtime throws SystemException. The ApplicationException is thrown by

a user program rather than the runtime. The SystemException includes the ExecutionEngineException, StaclOverFlowException etc. It is not recommended that we catch SystemExceptions nor is it good programming practice to throw SystemExceptions in our

applications.

System.OutOfMemoryException

System.NullReferenceException

Syste.InvalidCastException

Syste.ArrayTypeMismatchException

System.IndexOutOfRangeException

System.ArithmeticException

System.DevideByZeroException

System.OverFlowException User-Defined Exceptions

In C#, it is possible to create our own exception class. But Exception must be the ultimate base class for all exceptions in C#. So the user-defined exception classes must inherit from either

Exception class or one of its standard derived classes. //C#: Exception Handling: User defined exceptions

using System; class MyException : Exception {

public MyException(string str) { Console.WriteLine("User defined exception");}



} class MyClient


try { throw new MyException("RAJESH"); } catch(Exception e)

{Console.WriteLine("Exception caught here" + e.ToString()); } Console.WriteLine("LAST STATEMENT"); }

}

------------------x-------------------------x------------------------------x-------------------------x-----------------------

File Handling in C#

File handling is an unmanaged resource in your application system. It is outside your application domain (unmanaged resource). It is not managed by CLR.

Data is stored in two ways, persistent and non-persistent manner. When you open a file for reading or writing, it becomes stream.

Stream: Stream is a sequence of bytes traveling from a source to a destination over a communication path.

The two basic streams are input and output streams. Input stream is used to read and output stream is used to write.

The System.IO namespace includes various classes for file handling. The parent class of file processing is stream. Stream is an abstract class, which is used as the

parent of the classes that actually implement the necessary operations. The primary support of a file as an object is provided by a .NET Framework class called File. This

static class is equipped with various types of (static) methods to create, save, open, copy, move, delete, or check the existence of a file.



System.IO

System

System.IO

System.IO

Diagram to represent file-handling class hierarchy

The following table describes some commonly used classes in the System.IO namespace: -

Class Name Description

FileStream It is used to read from and write to any location within a file

BinaryReader It is used to read primitive data types from a binary stream

BinaryWriter It is used to write primitive data types in binary format

StreamReader It is used to read characters from a byte Stream

StreamWriter It is used to write characters to a stream

StringReader It is used to read from a string buffer

StringWriter It is used to write into a string buffer

DirectoryInfo It is used to perform operations on directories

FileInfo It is used to perform operations on files

Object

MarshalByref

Object

FileSystemInfo

FileInfo Directoryinfo File Path Directory DriveInfo



Reading and Writing in the text file

StreamWriter Class

The StreamWriter class in inherited from the abstract class TextWriter. The TextWriter class represents a writer, which can write a series of characters.

The following table describes some of the methods used by StreamWriter class : -

Methods Description

Close Close the current StreamWriter object and underlying stream

Flush Clears all buffers for the current writer and causes any buffered data to be written to the underlying stream.

Write Writes to the Stream

WriteLine Writes data specified by the overloaded parameters, followed by end of line.

Program to write user input to a file using StreamWriter Class

using System;

using System.Text; using System.IO; namespace FileWriting_SW

{ class Program

{

class FileWrite {

public void WriteData()

{ FileStream fs = new FileStream("c:\\test.txt", FileMode.Append, FileAccess.Write);

StreamWriter sw = new StreamWriter(fs); Console.WriteLine("Enter the text which you want to write to the file"); string str = Console.ReadLine();

sw.WriteLine(str); sw.Flush(); sw.Close();

fs.Close(); } }


{ FileWrite wr = new FileWrite();



wr.WriteData();

} } }

StreamReader Class

The StreamReader class is inherited from the abstract class TextReader. The TextReader class represents a reader, which can read series of characters.

The following table describes some methods of the StreamReader class: -

Methods Description

Close Closes the object of StreamReader class and the underlying stream, and

release any system resources associated with the reader

Peek Returns the next available character but doesn't consume it

Read Reads the next character or the next set of characters from the stream

ReadLine Reads a line of characters from the current stream and returns data as a string

Seek Allows the read/write position to be moved to any position with the file

Program to read from a file using StreamReader Class

using System;

using System.IO; namespace FileReading_SR

{

class Program {

class FileRead

{ public void ReadData()

{

FileStream fs = new FileStream ("c:\\test.txt", FileMode.Open, FileAccess.Read); StreamReader sr = new StreamReader (fs); Console.WriteLine("Program to show content of test file");

sr.BaseStream.Seek(0, SeekOrigin.Begin); string str = sr.ReadLine(); while (str != null)

{



Console.WriteLine(str); str = sr.ReadLine();

} Console.ReadLine(); sr.Close();

fs.Close(); } }

static void Main(string[] args) { FileRead wr = new FileRead();

wr.ReadData(); } }

}

Unsafe Mode When you use the new keyword to create a new instance of a reference type, you are asking the

CLR to set aside enough memory to use for the variable. The CLR allocates enough memory for the variable and associates the memory with your variable. Under normal conditions, your code is unaware of the actual location of that memory, as far as a memory address is concerned. After

the new operation succeeds, your code is free to use the allocated memory without knowing or caring where the memory is actually located on your system.

Occasionally, however, you need to work with a specific memory address in your C# code. Your code may need that extra ounce of performance, or your C# code may need to work with legacy code that requires that you provide the address of a specific piece of memory. The C# language

supports a special mode, called unsafe mode, which enables you to work directly with memory from within your C# code.

This special C# construct is called unsafe mode because your code is no longer safe from the memory-management protection offered by the CLR. In unsafe mode, your C# code is allowed to

access memory directly, and it can suffer from the same class of memory-related bugs found in C and C++ code if you're not extremely careful with the way you manage memory.

Generally, When we write any program in C#, we create managed code. Managed code is executed under the control of CLR. CLR causes that programmer do not need to manage memory and take care about memory’s allocation and deallocation. CLR also allows you to write

what is called ‘unsafe code’. The CLR knows how to manipulate three kinds of pointers:

Managed pointers: These pointers can point to data contained in the object heap managed by the garbage collector. These pointers are not used explicitly by the C# code. They are thus used implicitly by the C# compiler when it compiles methods with out and

ref arguments.

Unmanaged function pointers: The pointers are conceptually close to the notion of delegate.

Unmanaged pointers: These pointers can point to any data contained in the user addressing space of the process. The C# language allows to use this type of pointers in

zones of code considered unsafe.



Compilation options to allow unsafe code

Unsafe code must be used on purpose and you must also provide the /unsafe option to the csc.exe compiler to tell it that you are aware that the code you wish to compile contains zones

which will be seen as unverifiable by the JIT compiler. Visual Studio offers the Build Allow unsafe code project property to indicate that you wish to use this compiler option.

Declaring unsafe code in C# In C#, the unsafe keyword lets the compiler know when you will use unsafe code. It can be used

in three situations: Before the declaration of a class or structure. In this case, all the methods of the type can use

pointers. Before the declaration of a method. In this case, the pointers can be used within the body of this

method and in its signature. Within the body of a method (static or not). In this case, pointers are only allowed within the

marked block of code. For example: unsafe

{ ... }

Using pointers in C#

Each object, whether it is a value or reference type instance, has a memory address at which it is physically located in the process. This address is not necessarily constant during the lifetime of the object as the garbage collector can physically move objects store in the heap.

To create a pointer you can use the following declaration:

Type* variable_name; As a type may be used each type that is not a reference-type field. It can be only: sbyte, byte,

short, ushort, int, uint, long, ulong, char, float, double etc. Following examples show different pointers declarations:

int* pi; // declaration a pointer to integer variable float* pf, pq // two pointers to float variables char* pz // pointer to char

Advantages of UNSAFE in C#

Performance and flexibility, by using pointer you can access data and manipulate it in the most efficient way possible.

Compatibility, in most cases we still need to use old windows API’s, which use pointers extensively, or third parties may supply DLLs that some of its functions need pointer

parameters. Although this can be done by writing the DLLImport declaration in a way that avoids pointers, but in some cases it’s just much simpler to use pointer.

Memory Addresses, there is no way to know the memory address of some data without

using pointers.



Disadvantages of UNSAFE in C#

Complex syntax, to use pointers you need to go through more complex syntax than we used to experience in C#.

Harder to use, you need be more careful and logical while using pointers, miss -using pointers might lead to the following: -

- Overwrite other variables - Stack Overflow - Access areas of memory that doesn’t contain any data as they do.

- Overwrite some information of the code for the .net runtime, which will suerly lead your application to crash.

Your code will be harder to debug. A simple mistake in using pointers might lead your

application to crash randomly and unpredictably.

Type-safety, using pointers will cause the code to fail in the .net type-safety checks, and of course if your security police don’t allow non type-safety code, then the .net framework

will refuse to execute your application.

ADO.NET ADO.NET is a model used by .NET applications to communicate with a database for retrieving,

accessing and updating data. Features of ADO.NET

Some of the features of ADO.NET are given below:

1. Disconnected data architecture – ADO.NET uses the disconnected data architecture. Applications connect to the database only while retrieving and updating data. After data is retrieved, the connection with the databse is closed. When the database needs to be

updated, the connection is re-established. Working with applications that do not follow a disconnected architecure leads to a wastage of valuable system resources, since the application connects to the database and keeps the connection open until it stops

running, but does not actually interact with the database except while retrieving and updating data.

2. Data Cahed in datasets – A dataset is the most common method of accessing data since

it implements a disconnected architecture. Since ADO.NET is based on a disconnected data structure, it is not possible for the application to interact with the database for processing each record. Therefore, the data is retrieved and store in datasets. A dataset

is a chached set of database records.You can work with the records stored in a dataset as you work with real data; the only difference being that the dataset is independent of data source and you remain disconnected from the data source.

3. Data transfer in XML format – XML is the fundamental format for data transfer in ADO.NET. Data is transferred from a databse into a dataset and from the dataset to another component by using XML. You can use XML file as a data source and store data

from it in a dataset. Using XML as the data transfer language is beneficial as XML is an industry standard for exchanging information between types of applications.

4. Interaction with the database is done through data commands – All operations on the

database are performed by using data commands. A data command can be a SQL statement or a stored procedure. You can retrieve, insert, delete or modify data from a database by executing data commands.

The ADO.NET Object Model

ADO.NET uses a structured process flow containing components. The structured process flow or the object model is shown in following figure:



ADO.NET Object Model

Data Access in ADO.NET relies on two components: DataSet and Data Provider. DataSet

The dataset is a disconnected, in-memory representation of data. It can be considered as a local copy of the relevant portions of the database. The DataSet is persisted in memory and the data in

it can be manipulated and updated independent of the database. When the use of this DataSet is finished, changes can be made back to the central database for updating. The data in DataSet can be loaded from any valid data source like Microsoft SQL server database, an Oracle

database or from a Microsoft Access database.

Data Provider The Data Provider is responsible for providing and maintaining the connection to the database. A

DataProvider is a set of related components that work together to provide data in an efficient and performance driven manner.

The .NET Framework currently comes with two DataProviders: the SQL Data Provider which is designed only to work with Microsoft's SQL Server 7.0 or later and the OleDb DataProvider which allows us to connect to other types of databases like Access and Oracle. Each DataProvider

consists of the following component classes:

The Connection object which provides a connection to the database

The Command object which is used to execute a command

The DataReader object which provides a forward-only, read only, connected recordset

The DataAdapter object which populates a disconnected DataSet with data and performs update

Connection

Data Reader

Command

Data Adapter

.NET

Application

DataSet

Database

Data Provider

Accessing Retrieved data

Accessing retrieved data

Filling dataset w ith data

Establish connection

Executes a command

to retrieve data

Transfer data to the dataset and reflects the

changes in dataset

Retrieve data in a read-

only, forwarded only



Component classes that make up the Data Providers

The Connection Object The Connection object creates the connection to the database. Microsoft Visual Studio .NET

provides two types of Connection classes: the SqlConnection object, which is designed specifically to connect to Microsoft SQL Server 7.0 or later, and the OleDbConnection object, which can provide connections to a wide range of database types like Microsoft Access and

Oracle. The Connection object contains all of the information required to open a connection to the database.

The Command Object The Command object is represented by two corresponding classes: SqlCommand and

OleDbCommand. Command objects are used to execute commands to a database across a data connection. The Command objects can be used to execute stored procedures on the database, SQL commands, or return complete tables directly. Command objects provide three methods that

are used to execute commands on the database:

ExecuteNonQuery: Executes commands that have no return values such as INSERT,

UPDATE or DELETE

ExecuteScalar: Returns a single value from a database query

ExecuteReader: Returns a result set by way of a DataReader object

The DataReader Object

The DataReader object provides a forward-only, read-only, connected stream recordset from a database. Unlike other components of the Data Provider, DataReader objects cannot be directly instantiated. Rather, the DataReader is returned as the result of the Command object's

ExecuteReader method. The SqlCommand.ExecuteReader method returns a SqlDataReader object, and the OleDbCommand.ExecuteReader method returns an OleDbDataReader object. The DataReader can provide rows of data directly to application logic when you do not need to

keep the data cached in memory. Because only one row is in memory at a time, the DataReader provides the lowest overhead in terms of system performance but requires the exclusive use of an open Connection object for the lifetime of the DataReader.

The DataAdapter Object

The DataAdapter is the class at the core of ADO .NET's disconnected data access. It is essentially the middleman facilitating all communication between the database and a DataSet. The DataAdapter is used either to fill a DataTable or DataSet with data from the database with it's

Fill method. After the memory-resident data has been manipulated, the DataAdapter can commit the changes to the database by calling the Update method. The DataAdapter provides four properties that represent database commands:

SelectCommand

InsertCommand

DeleteCommand

UpdateCommand When the Update method is called, changes in the DataSet are copied back to the database and

the appropriate InsertCommand, DeleteCommand, or UpdateCommand is executed.



ADO.NET Archtecture

The following diagram illustrates the relationship between a .NET Framework data provider and a DataSet

Basic steps involved in data access with ADO.NET in disconnected environment

Data access using ADO.NET involves following steps:

Defining the connection string for the database server.

Defingin the connection to the database using connection string.

Defining the command or command string that contains the query.

Defining the data adapter using the command string and command object.

Creating a new dataset object.

If the command SELECT, filling the dataset object with the result of the query through the

data adapter.

Reading the records from the Data Tables in the datasets us ing the Data Row and Data Column Objects.

If the command is Update, Insert, or Delete, then updating the dataset through the data Adapter.

Accepting to save the changes in the data set to the database.

Connection methods:

Open- Opens the connection to our database.

Close- Closes the database connection.

Dispose- Realeses the resources on the connection object, used to force garbage collecting, ensuring no resources are being held after our connection is used. It automatically call close method.

State- Tells you what type of connection state your object is in used to check whether your conection is still using any resources.

If (ConnectionObject.Sate==Connectionstate.Open)



Command Object methods:

Execute Reader- Simply executes the SQL query against the database using Read().

ExecuteNonQuery- Used whenever you work with SQL stored procedures with parameters.

Execute Scalar-Returns a lightining fast signle value as an object from your database.

Ex: - object val = Command.ExecuteScalar();

Prepare- Equivalent to ADO’s Command.Prepare= TRUE property. Useful in caching the SQL command so it runs faster when called more than one.

Ex: - Commad.Prepare();

Dispose- Release the resources on the command object. Data Reader methods:

Read-Means the record pointer to the first row, which allows the data to be read by column Name of index position

Ex: - If (Reader.Read()==true);

IsClosed- A method that can determine if the Datareader is closed

If (DataReader.Isclosed==false);

Next Result-Equivalent to ADO’s NextRecordset method, where a batch of SQL

statement are executed with this method before advancing to the next set of data results. Ex: - DataReader.NextResult();

Close- close the Data Reader.

Example of Use of Command Object

It supports a command Type:

1. Text A SQL command defining the statements to be executed at the data source. 2. Stored Procedure The name of SP. You can use parameter property of a command to access input and output parameters and return values.

3. Table Direct the name of a table. Example Code1: -

Static void GetSalesByCategory( String ConnectionString, String CategoryName) {

Using (SqlConnection connection= New SqlConnection(ConnectionString)) { SqlCommand command = new Sqlcommand();

Command.Connection=connection; Command.CommandText=”SalesByCategory”; Command.CommandType=CommandType.StoredProcedure;

SqlParameter parameter = New SqlParameter(); parameter.ParameterName=”@ CategoryName”; parameter.SqlDbType=SqlDbType.Nvarchar;

parameter.Direction=ParameterDirection.Input; parameter.Value= CategoryName; Command.Parameters.Add(parameter);

Connection.Open(); SQLDataReader.reader=Command.ExecuteReader(); If (reader.HasRows)

{ While(reader.Read())



{ Console.WriteLine(“{0}:{1}”, reader[0],reader[1]);

} } else

{ Console.WriteLine(“No rows found”);} reader.Close();

}

} Example Code2:

//Use of DataTable to Display the content of Database

using System.Data.OleDb;

namespace Ex_DatabaseDemo

{

class Program {


{

OleDbConnection con = new

OleDbConnection(@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=D:\

\Ex_TestDataBase.mdb");

OleDbDataAdapter adp = new OleDbDataAdapter("Select * from

EMP", con);

DataTable tbl = new DataTable();

adp.Fill(tbl);

DataRow row;

for (int i = 0; i < 5; i++)

{

row = tbl.Rows[i];

for (int j = 0; j < 5; j++)

Console.Write("{0,15}", row[j]);

Console.WriteLine();

}

Console.Read();

}

}

}

Example Code3:

using System.Data.SQLClient;

namespace Ex_DatabaseDemo

{

class Program {


{

String OleDbConnectionString=Provider=SQLOLEDB; Data Source=(local);”+

“Inegrated Security=SSPI;Initial Catalog=AdventureWorks;”;



String OleDbSelect = “Select * from Sales.SalesOrderHeader Where

TotalDues>?”;

OleDbConnection oledbconection = new OleDbConnection(OleDbConnection

String);

OleDbCommand oledbcommand = new OleDbCommand(OleDbSelect,

oledbconection);

OleDbCommand.Parameters.Add(“@TotalDue”,OleDbType.Currency);

OleDbCommand.Parameters[“@TotalDue”].Value= 20000;

OleDbDataAdapter OleDbDa = new OleDbDataAdapter(oledbcommand);

DataTable OleDbDt = new DataTable();

OleDbDa.Fill(OleDbDt);

ForEach(DataRow row in OleDbDt.Rows)

{

Console.WriteLine(row[“SalesOrderID”]);

Console.WriteLine(row[“OrderDate”]);

Console.WriteLine(row[“TotalDue”]);

}

Console.Read();

}

}



Generics

Generics are a new feature in version 2.0 of the C# language and the common language runtime

(CLR). Generics introduce to the .NET Framework the concept of type parameters, which make it possible to design classes and methods that defer the specification of one or more types until the class or method is declared and instantiated by client code. For example, by using a generic type

parameter T you can write a single class that other client code can use without incurring the cost or risk of runtime casts or boxing operations, as shown here:

Example: // Declare the generic class

public class GenericList<T> { void Add(T input) { }

} class TestGenericList {

private class ExampleClass { } static void Main() {

// Declare a list of type int GenericList<int> list1 = new GenericList<int>();

// Declare a list of type string GenericList<string> list2 = new GenericList<string>(); // Declare a list of type ExampleClass

GenericList<ExampleClass> list3 = new GenericList<ExampleClass>(); } }

Generics Overview

Use generic types to maximize code reuse, type safety, and performance.

The most common use of generics is to create collection classes.

The .NET Framework class library contains several new generic collection classes in the

System.Collections.Generic namespace. These should be used whenever possible in place of classes such as ArrayList in the System.Collections namespace.

You can create your own generic interfaces, classes, methods, events and delegates.

Generic classes may be constrained to enable access to methods on particular data

types.

Information on the types used in a generic data type may be obtained at run-time by means of reflection.



As the projects get more complicated, programmers increasingly need a means to better reuse and customize their existing component-based software. To achieve such a high level of code

reuse in other languages, programmers typically employ a feature called Generics. Using Generics, we can create class templates that support any type. When we instantiate that

class, we specify the type we want to use, and from that point on, our object is "locked in" to the type we chose.

Let us look at an example of how we can create a generic class using C# 2.0. public class MyCustomList<MYTYPE>

{ private ArrayList m_list = new ArrayList(); public int Add(myType value)

{ return m_list.Add(value); }

public void Remove(myType value) {

m_list.Remove(value); }

public myType this[int index] { get

{ return (myType)m_list[index]; }

set { m_list[index] = value;

} } }

Here, MyCustomList is built on an ArrayList. But its methods and indexer are strongly typed. Here <myType> is really just a placeholder for whatever type you choose when you create the class.

This placeholder is defined in angled brackets after the name of the class. Now, let us look at how to create an instance of the class MyCustomList:

MyCustomList<int> list = new MyCustomList<int>(); // Add two integers to list

list.Add(1); list.Add(33); // The next statement will fail and wont compile

list.Add("Emp"); If we want our MyCustomList to store strings, it can be done as follows:

MyCustomList<string> list = new MyCustomList<string>();



Generic Methods

Generic methods use a similar syntax to generic types. They allow individual methods to be created that work with types that are defined only when the method is called. A generic method includes one or more type parameters in its signature. Those type parameters can then be used

for the return value for the method and in its parameters. This allows the methods to be reused with many different types.

Code Example: - 1 // GenericMethod.cs

2 // Using overloaded methods to print arrays of different types. 3 using System; 4 using System.Collections.Generic;

5 6 class GenericMethod 7 {

8 static void Main( string[] args ) 9 { 10 // create arrays of int, double and char

11 int[] intArray = { 1, 2, 3, 4, 5, 6 }; 12 double[] doubleArray = { 1.1, 2.2, 3.3, 4.4, 5.5, 6.6, 7.7 }; 13 char[] charArray = { 'H', 'E', 'L', 'L', 'O' };

14 15 Console.WriteLine( "Array intArray contains:" ); 16 PrintArray( intArray ); // pass an int array argument

17 Console.WriteLine( "Array doubleArray contains:" ); 18 PrintArray( doubleArray ); // pass a double array argument 19 Console.WriteLine( "Array charArray contains:" );

20 PrintArray( charArray ); // pass a char array argument 21 } // end Main 22

23 // output array of all types 24 static void PrintArray< E >( E[] inputArray ) 25 {

26 foreach ( E element in inputArray ) 27 Console.Write( element + " " ); 28

29 Console.WriteLine( "\n" ); 30 } // end method PrintArray 31 } // end class GenericMethod

Output:

Array intArray contains: 1 2 3 4 5 6

Array doubleArray contains: 1.1 2.2 3.3 4.4 5.5 6.6 7.7

Array charArray contains:H E L L O

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