1.1_introduction to java

8/7/2019 1.1_Introduction to Java

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Introduction to

Java


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Session Objectives

Determine Programming Models

Features Of Object Oriented Programming Model

Encapsulation

Data Abstraction

Inheritance

Polymorphism

History of Java

Features of Java

Java vs C++

Types of Java Programs


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Programming Models

Procedural programming model - Each problem is divided into smallerproblems and solved using specified modules that act on data

Object-oriented programming model It perceives theentiresoftwaresystem as a collection of objects which contain attributes and behaviors.


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Object Oriented ProgrammingModel

Encapsulation - Encapsulation hides the implementation details of anobject and thereby, hides its complexity.

Data Abstraction It hides the implementation of the data belonging toan object.

Inheritance - Inheritance creates a hierarchy of classes and helps inthe reuse of the attributes and methods of class.

Polymorphism Polymorphism triggers different reactions in objects inresponse to thesame message.


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Encapsulation

Data

Hiding


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Data Abstraction

Hiding

Implementation

details of the

Data


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Inheritance

Derived class

inherits

features from

Base Class


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History of Java

Java began as Programming Language Oak.

Oak - Developed by members of Green Project, which included James Goslingand 2 more people in 1991 to create products forelectronics market.

Existing programming languages were not suited for thesame.

Chief Programmer of Sun Microsystems, James Gosling, was given the task of

creating software for controlling consumerelectronic devices.The requirement of Software was to run on different kinds of computers,should

have power of networks and be based on web.

Members of the Oak team realized that Java would provide the required crossplatform independence that is independent from hardware,network and OS.


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Features of Java

Java is an Internet programming language:

Java programs can be used to access data existingacross the network irrespective of thesource platform

Java is secure:

Due to thestrong type-checking done by Java anychanges made to the program are tagged aserrors andthe program will not execute. Java is, therefore,secure


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Java is a platform independent language:

The Java compiler compiles Java code to an intermediate

bytecode that is understood by the Java environment. The

bytecode can be executed by the Java interpreter or anyJava-enabled Internet browser

Due to the bytecode compilation process and its

interpretation by a browser, Java programs can be executed

on various hardware and operating systems


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Java is a high-performance language:

Java programs are comparable in speed to the programswritten in other compiler-based languages like C and C++.

Java programs are faster than the programs written in otherinterpreter-based languages, such as BASIC

Java is simple:

The syntax of Java is similar to C++. Java does not support

pointers, multiple inheritance, goto statement, and operatoroverloading

Features that slow down application development cycle havebeen omitted in Java


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Java Memory Management

Java prevents errors that arise due to improper memory

usage because in Java, programmers do not need tomanipulate memory


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Java vs. C++:

Java is a pure object-oriented language because every

statement in Java is written inside a class. In C++, the

main() method is always written outside any classIn Java, all the data types except the primitive types are

objects. Even the primitive data types can be

encapsulated inside classes

Data types:

Java has two additional primitive data types besides the

ones available in C++


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The byte data type of Java occupies one byte of memory space

and can store integral numbers

The other data type boolean can store any one of the two

boolean values, true and false Java omits pointers and structs that are available in C++

In Java, the char data type stores characters in Unicodeformat unlike the 8-bit ASCII format in C++. Unicode is a

16-bit character format that can store Asian languagealphabets

Data types in Java have a fixed size, regardless of theoperating system used


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Constructs:

In Java, the constructs such as if...else, while, anddo...while take expressions that result in a boolean value

The switch construct and the for loop in Java are similar totheir counterparts in C++

Inheritance:

Java does not support multiple inheritance

All classes in Java are derived from Object class

To inherit from a class, you use the extends keyword


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Method Overloading:

Java allows method overloading but does not support

operator overloading

Arrays:In C++, an array is a collection of elements where as

in Java, arrays are real objects because you can

allocate memory to an array using the new operator

In Java, array accesses are checked to ensure that theindices are within the range of the array


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JavaPrograms

Java programs fall into two categories, Applications and Applets

Applications

Execute from any operating system prompt

They can beeither window-based applications orconsole applications

They have moresecurity privileges than applets

They reside on the hard disk of a local machine


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Java Programs (Contd.)

Applets

Execute in a Java-enabled browser

They are window-based

They can access the resources of the host machineonly, they cannot access the files on the computer towhich they are downloaded

They reside on a remote machine


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SampleApplication:- Welcome.java

public class Welcome

{

public static void main(String args[])

{

System.out.println(Hello);

}

}


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In Java, the main() method and the class in which it is

defined should be declared public because the Java

runtime environment has to access the main() method to

execute a programThe main() method should be declared static because it

has to exist before any object of the class is created

The command line parameter is a String type variable

main(String args[]). The number of arguments is

determined by the String class object


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The String Object:

In Java, a String is a real object and not an array of null-

terminated characters as in C++

In Java, the String objects are consistent. The way in

which strings are obtained and the string elements areaccessed is consistent across all systems. They have well-

defined programming interfaces

In Java, the String objects are reliable. They do not give

rise to memory leaks in a program


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Java uses all the system resources such as the display deviceand the keyboard with the help of the System class. This classcontains all the methods that are required to work with the

system resourcesThe out object encapsulated inside the System classrepresents the standard output device. This object contains the

println() method

The println() method displays data on the screen


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Executing a Java Program:

Java programs are executed by a program called the Java

Virtual Machine (JVM). The JVM contains the runtime

environment and the class loader

You must save a Java source file with the .java extension.

The name of the file should be the same as the public class

name

When you compile a .java file, a .class file is created


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To compile a file, you use thejavac utility.

To execute a .class file, you use the java utility

For example, to compile and execute a class Welcome:

Save the file as Welcome.java

At the command prompt, type

javac Welcome.java At the command prompt, type

java Welcome

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