chapter 11 object-oriented design

Chapter 11 Object-Oriented Design

Chapter 7 Objects and Classes

Chapter 8 Strings and Text I/O

Chapter 9 Inheritance and Polymorphism

Chapter 6 Arrays

§10.2, “Abstract Classes”

§10.4, “Interfaces”

Chapter 13 Graphics

Chapter 14 Event-Driven Programming

Chapter 17 Exceptions and Assertions

Chapter 18 Binary I/O

Exception and binary I/O can be covered after Chapter 9

GUI can be covered after §10.2, “Abstract Classes” Chapter 12 GUI Basics

Chapter 11 Object-Oriented Design

Objectives from book To become familiar with the process of program development

(§11.2). To the relationship types: association, aggregation, composition,

strong inheritance, and weak inheritance (§11.3). To declare classes to represent the relationships among the classes

(§11.3). To design systems by identifying the classes and discovering the

relationships among these classes (§11.4). To implement the Rational class and process rational numbers

using this class (§11.5). To design classes that follow the class-design guidelines (§11.6). To model dynamic behavior using sequence diagrams and

statechart diagrams (§11.7 Optional) To know the concept of framework-based programming using Java

API (§11.8).

My Objectives

Object Oriented Modeling Discuss real world experience

– Network management System– PDA Products

Unit Testing

Software Development Process Requirement Specification

System Analysis

System Design

Testing

Implementation

Maintenance

Deployment

Requirement Specification Requirement Specification

System Analysis

System Design

Testing

Implementation

Maintenance

Deployment

A formal process that seeks to understand the problem and document in detail what the software system needs to do. This phase involves close interaction between users and designers.

Most of the examples in this book are simple, and their requirements are clearly stated. In the real world, however, problems are not well defined. You need to study a problem carefully to identify its requirements.

System AnalysisRequirement Specification

System Analysis

System Design

Testing

Implementation

Maintenance

Deployment

Seeks to analyze the business process in terms of data flow, and to identify the system’s input and output.

Part of the analysis entails modeling the system’s behavior. The model is intended to capture the essential elements of the system and to define services to the system.

System Design Requirement Specification

System Analysis

System Design

Testing

Implementation

Maintenance

Deployment

The process of designing the system’s components.

This phase involves the use of many levels of abstraction to decompose the problem into manageable components, identify classes and interfaces, and establish relationships among the classes and interfaces.

Implementation Requirement Specification

System Analysis

System Design

Testing

Implementation

Maintenance

Deployment

The process of translating the system design into programs. Separate programs are written for each component and put to work together.

This phase requires the use of a programming language like Java. The implementation involves coding, testing, and debugging.

Testing Requirement Specification

System Analysis

System Design

Testing

Implementation

Maintenance

Deployment

Ensures that the code meets the requirements specification and weeds out bugs.

An independent team of software engineers not involved in the design and implementation of the project usually conducts such testing.

Deployment Requirement Specification

System Analysis

System Design

Testing

Implementation

Maintenance

Deployment

Deployment makes the project available for use.

For a Java applet, this means installing it on a Web server; for a Java application, installing it on the client's computer.

Maintenance Requirement Specification

System Analysis

System Design

Testing

Implementation

Maintenance

Deployment

Maintenance is concerned with changing and improving the product.

A software product must continue to perform and improve in a changing environment. This requires periodic upgrades of the product to fix newly discovered bugs and incorporate changes.

Software Methodologies

Waterfall Model Evolutionary Model Incremental Model Agile Methodology

Waterfall Model Top-down Development steps are executed sequentially Gate approvals between consecutive steps Documentation oriented Advantages:

– simple for management Disadvantage:

– Documents are costly to produce and approve. – Some steps would get frozen prematurely

Not developing what the customer wants Being inflexible to change.

Evolutionary Model Performs all processes in at least 2 passes First pass implements only those requirements that

are firm or known. Negotiates with the customer after the completion

of a pass before the next pass begins. Advantage:

– Developing requirements incrementally – meeting the customer’s immediate needs.

Disadvantage– resulting system architecture is often corrupted.

Incremental Model customers identify the system features and prioritize them. Development prioritizes delivery increments. Each successive delivery includes an enlarging subset of the feature

list. Requirements of the first increment are frozen, development proceeds

in detail on the increment. Concurrently consider requirement changes for the next increment Advantage:

– Enables faster delivery to the customer who in turn gains experience on the system and provide feedback for later increments.

– Lower risk of overall project failure . top priority features are delivered first - tested more

thoroughly by the development organization as well as in operation.

Agile Principles:

– Individuals and interactions over processes and tools – Working software over comprehensive documentation – Customer collaboration over contract negotiation– Responding to change over following a plan

Goals: – Accept customer changes any time; – have short daily communications between customers and

developers, – develop and deliver small increments in lieu of one release as at

the end of the waterfall model. Advocates putting top developers in a bullpen and let the team self

organize. Problem: Documentation is definitely downplayed.

Small Projects (< 10 )

Observations Waterfall model is a conceptual model Personally have worked on combination of

waterfall, incremental, and evolutionary Maintenance is 80% of the life cycle cost

– Problems? Documentation Institutional knowledge

Software industry often reinvents the wheel

Some challenges on Software Architecture

Network Management System PDA

Optical network and Network Management

Wide Area Network

EMS NMS EMS

Network Management System Example

An optical communication network using SDH Network management system another network using

TMN Diverse nodes with common functions and differing in

hardware, functionalities, and capacities Developed by globally distributed teams Development of releases transitioned successfully from

one team to another Two key factors are product line architecture;

incremental and iterative development

Product Architecture to Product Line Architecture

Each delivery is custom-tailored Paradigm shift: Product Development

House to Product Line Platform to generate similar products with custom options.

Benefits – reuse

Software Architecture – Logical View

Database for– Configuration Management – on individual network

configuration– Account management – for end customers

Superclass and subclasses– NE common properties – NE specific properties– New NE’s just inherit the common properties and

override those that are specific

Applications PDA: From calendar, address book, calculator,

notes, spreadsheet To

– exchange business cards– internet– email– instant messaging – on-line search– VoIP– GPS– camera etc.

Relationships among Classes

Association Aggregation Composition Inheritance

Other Applications

n-tier architectures: GUI, server, and DB

Back to OOM

OOM concepts

Association Association represents a general binary relationship that describes an activity between two classes.

Student * 5..60

Take Teach 0..3 1

Teacher Faculty Course

public class Student { /** Data fields */ private Course[] courseList; /** Constructors */ /** Methods */ }

public class Course { /** Data fields */ private Student[]

classList; private Faculty faculty; /** Constructors */ /** Methods */ }

public class Faculty { /** Data fields */ private Course[] courseList; /** Constructors */ /** Methods */ }

An association is usually represented as a data field in the class.

Translation is not Unique

NOTE: If you don’t need to know the courses a student takes or a faculty teaches, the data field courseList in Student or Faculty can be omitted.

Association Between Same Class

Association may exist between objects of the same class. For example, a person may have a supervisor.

Person Supervisor

Aggregation and CompositionAggregation is a special form of association, which represents an ownership relationship between two classes. Aggregation models the has-a relationship. If an object is exclusively owned by an aggregated object, the relationship between the object and its aggregated object is referred to as composition.

Name Address Person

Composition Aggregation

Representing Aggregation in ClassesAn aggregation relationship is usually represented as a data field in the aggregated class.

public class Name { /** Data fields */ /** Constructors */ /** Methods */ }

public class Person { /** Data fields */ private Name name; private Address address; /** Constructors */ /** Methods */ }

public class Address { /** Data fields */ /** Constructors */ /** Methods */ }

Inner Classes TranslationIf Name or Address is used in the Person class only, they can be declared as an inner class in Person. For example,

public class Person { private Name name; private Address address; ... class Name { ... } class Address { ... }}

InheritanceInheritance models the is-an-extension-of relationship between two classes.

Person Faculty

public class Faculty extends Person { /** Data fields */ /** Constructors */ /** Methods */ }

(A) (B)

Weak Inheritance RelationshipA weak is-an-extension-of relationship can be represented using interfaces. For example, the weak is-an-extension-of relationship “students are comparable based on their grades” can be represented by implementing the Comparable interface, as follows:

Person Student

Comparable

public class Student extends Person implements Comparable { /** Data fields, Constructors, and */ /** Methods */ /** Implement the compareTo method */ public int compareTo(Object object) { // ... } }

(A) (B)

Class Design

1. Identify classes for the system.

2. Describe attributes and methods in each

class.

3. Establish relationships among classes.

4. Create classes.

Example 11.1 Borrowing Loans

Name BorrowerPersonLoan Address

Borrower -loan: Loan +Borrower() +Borrower(name: Name, address: Address) +getLoan(): Loan +setLoan(loan: Loan): void +toString(): String

Address -street: String -city: String -state: String -zip: String +Address() +Address(street: String, city: String, state: String, zip: String) +getStreet(): String +getCity(): String +getState(): String +getZip(): String +setStreet(street: String): void +setCity(city: String): void +setState(state: String): void +setZip(zip: String): void +getFullAddress(): String

Defined in Example 6.7

Person -name: Name -address: Address +Person() +Person(name: Name, address: Address) +getName(): Name +seName(name: Name): void +getAddress(): Address +setAddress(address: Address): void +toString(): String

Name -firstName: String -mi: char -lastName: String +Name() +Name(firstName: String, mi: char, lastName: String) +getFirstName(): String +getMi(): char +getLastName(): String +setFirstName(firstName: String): void +setMi(mi: char): void +setLastName(lastName: String): void +getFullName(): String

Example 11.1 Borrowing Loans, cont.

The following is a test program that uses the classes Name, Person, Address, Borrower, and Loan.

BorrowLoan Run

Example 11.2 The Rational Class

Rational RunTestRationalClass

1 Add, Subtract, Multiply, Divide

Rational -numerator: long -denominator: long +Rational() +Rational(numerator: long, denominator: long) +getNumerator(): long +getDenominator(): long +add(secondRational: Rational): Rational +multiply(secondRational: Rational): Rational +subtract(secondRational: Rational): Rational +divide(secondRational: Rational): Rational +toString(): String -gcd(n: long, d: long): long

java.lang.Number +byteValue(): byte +shortValue(): short +intValue(): int +longVlaue(): long +floatValue(): float +doubleValue():double

java.lang.Comparable compareTo(Object): int

Class Design Guidelines Designing a Single Class.

Using Modifiers public, protected, private and static

Using Inheritance or Aggregation Using Interfaces or Abstract Classes

Designing a Class A class should describe a single entity or a set of

similar operations. Break a single entity with too many

responsibilities into several classes to separate responsibilities.

Example: The String class, StringBuffer class, and StringTokenizer class all deal with strings, but have different responsibilities.

Designing a Class, cont. Classes are usually designed for use by a wide

range of applications– Provide a variety of ways for customization through

properties and methods.

Designing a Class, cont. Classes are designed for reuse. Users can incorporate classes in many different

combinations, orders, and environments.

Hence design a class that – DON’T: imposes restrictions on what or when the user

can do with it,

– DO: ensure that properties can be set in any order, with any combination of values, and methods function independently of their order of occurrence.

Designing a Class, cont. Provide a public no-arg constructor Override the equals method and the toString method

defined in the Object class whenever possible.

Designing a Class, cont. Follow standard Java programming style and

naming conventions. – Choose informative names for classes, data

fields, and methods.

– Always place the data declaration before the constructor,

– and place constructors before methods.

– Always provide a constructor and initialize variables to avoid programming errors.

Using Visibility Modifiers Each class can present two contracts:

– one for the users of the class – one for the extenders of the class.

Make fields private and accessor methods public if they are intended for the users of the class.

Make the fields or method protected if they are intended for extenders of the class.

The contract for the extenders encompasses the contract for the users.

The extended class may increase the visibility of an instance method from protected to public, or change its implementation, but you should never change the implementation in a way that violates that contract.

Using Visibility Modifiers, cont. Use the private modifier to hide its data from direct

access by clients. Use get methods and set methods to provide users

with access to the private data, but only to private data you want the user to see or to modify.

Hide methods not intended for client use. – Example 11.2: gcd method in the Rational class is private

because it is only for internal use within the class.

Using the static Modifier

A property that is shared by all the instances of the class should be declared as a static property.

Using Inheritance or Aggregation?

inheritance versus aggregation =is-an-extension-of relationship versus has-a relationship. Example: an apple is fruit; so use inheritance to model the relationship between the classes Apple and Fruit. Example: A person has a name; so use aggregation to model the relationship between the classes Person and Name.

Using Inheritance or Aggregation? cont.

The choice between inheritance and aggregation is not always obvious. Example: we used inheritance to model the relationship between the classes Circle and Cylinder. But … if you argue that a cylinder consists of circles; thus, you might use aggregation to define the Cylinder class as follows:

Using Inheritance or Composition, cont.

public class Cylinder { private Circle circle; /** Constructors */ /** Methods */}

Using Inheritance or Aggregation? cont.

Both designs are fine. Which one is preferred? If polymorphism is desirable, you need to use the inheritance design. If you don’t care about polymorphism, the aggregation design gives more flexibility because the classes are less dependent using aggregation than using inheritance.

Using Interfaces or Abstract Classes?

Both interfaces and abstract classes can be used to generalize common features. How do you decide whether to use an interface or a class? In general, a strong is-an-extension-of relationship that clearly describes a parent-child relationship should be modeled using classes.

Using Interfaces or Abstract Classes, cont.

Example: An orange is a fruit:

– Model their relationship using class inheritance. A weak is-an-extension-of relationship, also known as an is-kind-of relationship, indicates that an object possesses a certain property.

– Model a weak is-an-extension-of relationship with interfaces.

– All strings are comparable, so the String class implements the Comparable interface.

– A circle or a rectangle is a geometric object, so Circle can be designed as a subclass of GeometricObject.

– Circles are different and comparable based on their radius, so Circle can implement the Comparable interface.

Using Interfaces or Abstract Classes, cont.

Interfaces are more flexible than abstract classes– a subclass can extend only one superclass, but

implement any number of interfaces. Interfaces cannot contain concrete methods.

– combine the virtues of interfaces and abstract classes by creating an interface with a companion abstract class that implements the interface. So you can use the interface or its companion class whichever is more convenient.

Sequence diagramsSequence diagrams describe interactions among objects by depicting the time ordering of method invocations.

anObject: TheClass Class role

Method Invocation

Activation

anotherObject: TheOtherClass

Method InvocationanotherMethod()

aMethod()

Sequence diagrams, cont.

name: Name : BorrowLoan address: Address loan: Loan borrower: Borrower

setFirstName

setLastName

setStreet

setCity

setState

setZip

setAnnualInterestRate

setNumOfYears

setLoanAmount

setName

setAddress

setLoan

Statechart diagramsStatechart diagrams describe flow of control of the object.

IndicateInitial State

Transition

State1

State2

Statechart diagrams, cont.

Class Loaded

JVM loads the class for the object

Use the new operator to create the object

Object Created

Invoke the finalize method on the object

Object Destroyed

Supplement P: Designing Generic Matrix Classes

Objective: This example gives a generic class for matrix arithmetic. This class implements matrix addition and multiplication common for all types of matrices.

GenericMatrix

Example 11.3, cont.

GenericMatrix -matrix: Object[][] #GenericMatrix(matrix: Object[][]) +getMatrix(): Object[][] +setMatrix(matrix: Object[][]): void +addMatrix(secondMatrix: Object[][]): Object[][] +multiplyMatrix(secondMatrix: Object[][]): Object[][] +printResult(m1: GenericMatrix, m2: GenericMatrix, m3: GenericMatrix, op: char): void #createGenericMatrix():GenericMatrix #add(o1: Object, o2: Object): Object #multiply(o1: Object, o2: Object): Object #zero():Object

IntegerMatrix

RationalMatrix

Example 11.3, cont.

Objective: This example gives two programs that utilize the GenericMatrix class for integer matrix arithmetic and rational matrix arithmetic.

TestIntegerMatrix Run

TestRationalMatrix RunRationalMatrix

IntegerMatrix

The Java API

The Java API (Application Program Interface, Application Programming Interface, or Application Programmer interface) consists of numerous classes and interfaces grouped into more than a dozen of packages. You have used classes and interfaces in the java.lang, javax.swing, and java.util packages.

Framework-Based ProgrammingTo create comprehensive projects, you have to use more classes and interfaces in the Java API. The classes and interfaces in the Java API establish a framework for programmers to develop applications using Java. For example, the classes and interfaces in the Java GUI API establish a framework for developing GUI programs. You have to use these classes and interfaces and follow their conventions and rules to create applications. This is referred to as framework-based programming.

Framework-Based Programming, cont.

Once you understand the concept of Java and object-orient programming, the most important lesson from now on is learning how to use the API to develop useful programs. The most effective way to achieve it is to imitate good examples. The book provides many carefully designed examples to demonstrate the concept of the framework-based programming using the Java API.

Framework-Based Programming, cont.

You will learn the Java GUI programming framework in Part III, the Java exception handling framework in Chapter 17, the Java IO framework in Chapter 18, the Java collections framework in Chapter 22, the Java multithreading framework in Chapter 24, Networking in Chapter 25, Internationalization in Chapter 26, and JDBC in Chapters 32-33, Servlets in Chapter 34and RMI in Chapter 36.

chapter 11 object-oriented design

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