oracle10g java programming instructor guide - volume 1.pdf

7/25/2019 Oracle10g Java Programming Instructor Guide - Volume 1.pdf

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D17249GC11

Edition 1.1

August 2004

D39815

Oracle10g: Java Programming

Instructor Guide - Volume 1


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Copyright 2004, Oracle. All rights reserved.

This documentation contains proprietary information of Oracle Corporation. It is

provided under a license agreement containing restrictions on use and disclosure and

is also protected by copyright law. Reverse engineering of the software is prohibited.

If this documentation is delivered to a U.S. Government Agency of the Department of

Defense, then it is delivered with Restricted Rights and the following legend is

applicable:

Restricted Rights Legend

Use, duplication or disclosure by the Government is subject to restrictions for

commercial computer software and shall be deemed to be Restricted Rights software

under Federal law, as set forth in subparagraph (c)(1)(ii) of DFARS 252.227-7013,

Rights in Technical Data and Computer Software (October 1988).

This material or any portion of it may not be copied in any form or by any means

without the express prior written permission of Oracle Corporation. Any other copying

is a violation of copyright law and may result in civil and/or criminal penalties.

If this documentation is delivered to a U.S. Government Agency not within the

Department of Defense, then it is delivered with Restricted Rights, as defined in

FAR 52.227-14, Rights in Data-General, including Alternate III (June 1987).

The information in this document is subject to change without notice. If you find any

problems in the documentation, please report them in writing to Education Products,

Oracle Corporation, 500 Oracle Parkway, Box SB-6, Redwood Shores, CA 94065.Oracle Corporation does not warrant that this document is error-free.

All references to Oracle and Oracle products are trademarks or registered trademarks

of Oracle Corporation.

All other products or company names are used for identification purposes only, and

may be trademarks of their respective owners.

Authors

Jeff Gallus

Glenn Stokol

Technical Contributors

and Reviewers

Kenneth CooperPeter DriverChristian DugasCraig HollisterChika IzumiPete LaseauGlenn MaslenMonica MotleyGayathri Rajagopal

Publisher

Poornima G


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Preface

I Introduction

Objectives I-2

Course Overview I-3

1 Introducing the Java and Oracle Platforms

Objectives 1-2

What Is Java? 1-3

Key Benefits of Java 1-4

An Object-Oriented Approach 1-6

Platform Independence 1-7

Using Java with Enterprise Internet Computing 1-8

Using the Java Virtual Machine 1-10

How Does JVM Work? 1-12

Benefits of Just-In-Time (JIT) Compilers 1-14

Implementing Security in the Java Environment 1-16

Deployment of Java Applications 1-18

Using Java with Oracle 10g 1-19

Java Software Development Kit 1-20

Using the Appropriate Development Kit 1-21

Integrated Development Environment 1-22

Exploring the JDeveloper Environment 1-23

Oracle10g Products 1-24

Summary 1-25

2 Defining Object-Oriented Principles

Objectives 2-2

What Is Modeling? 2-4

What Are Classes and Objects? 2-5

An Objects Attributes Maintain Its State 2-6

Objects Have Behavior 2-8

Objects Are Modeled as Abstractions 2-9

Defining Object Composition 2-11

The Donut Diagram 2-13

Guided Practice: Spot the Operations and Attributes 2-14Collaborating Objects 2-15

Objects Interact Through Messages 2-16

What Is a Class? 2-17

How Do You Identify a Class? 2-18

Comparing Classes and Objects 2-19

What Is Encapsulation? 2-21

What Is Inheritance? 2-22

Contents

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Using the Is-a-Kind-of Relationship 2-23

What Is Polymorphism? 2-24

Architecture Rules for Reuse 2-26

Engineering for a Black Box Environment 2-27

Order Entry UML Diagram 2-28

Summary 2-29

Practice 2: Overview 2-30Order Entry System Partial UML Class Model 2-33

3 Basic Java Syntax and Coding Conventions

Objectives 3-2

Examining Toolkit Components 3-4

Exploring Packages in J2SE/J2EE 3-5

Documenting Using the J2SE 3-6

Contents of a Java Source 3-7

Establishing Naming Conventions 3-8

More About Naming Conventions 3-10

Defining a Class 3-12Rental Class: Example 3-13

Creating Code Blocks 3-15

Defining Java Methods 3-16

Examples of a Method 3-17

Declaring Variables 3-18

Examples of Variables in the Context of a Method 3-19

Rules for Creating Statements 3-20

What Are JavaBeans? 3-21

Managing Bean Properties 3-22

Exposing Properties and Methods 3-23JavaBean Standards at Design Time 3-24

Compiling and Running a Java Application 3-25

The CLASSPATHVariable 3-26

CLASSPATH: Example 3-27

Summary 3-28

Practice 3: Overview 3-29

4 Exploring Primitive Data Types and Operators

Objectives 4-2

Reserved Keywords 4-4

Variable Types 4-5Primitive Data Types 4-7

What Are Variables? 4-9

Declaring Variables 4-10

Local Variables 4-11

Defining Variable Names 4-12

What Are Numeric Literals? 4-13

What Are Nonnumeric Literals? 4-15

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Guided Practice: Declaring Variables 4-17

What Are Operators? 4-19

Categorizing Operators 4-20

Using the Assignment Operator 4-21

Working with Arithmetic Operators 4-22

More on Arithmetic Operators 4-23

Examining Conversions and Casts 4-24Incrementing and Decrementing Values 4-26

Relational and Equality Operators 4-27

Using the Conditional Operator (?:) 4-28

Using Logical Operators 4-29

Compound Assignment Operators 4-30

Operator Precedence 4-31

More on Operator Precedence 4-32

Concatenating Strings 4-33

Summary 4-34


5 Controlling Program Flow

Objectives 5-2

Categorizing Basic Flow Control Types 5-4

Using Flow Control in Java 5-6

Using the i f Statement 5-7

Nesting i f Statements 5-8

Guided Practice: Spot the Mistakes 5-9

Defining the swi t ch Statement 5-10

More About the swi t ch Statement 5-12

Looping in Java 5-13Using the whi l e Loop 5-14

Using the dowhi l e Loop 5-15

Using the f or Loop 5-16

More About the f or Loop 5-17

Guided Practice: Spot the Mistakes 5-18

The br eak Statement 5-19

Summary 5-20


6 Building Applications with Oracle JDeveloper 10g

Objectives 6-2What Is Oracle JDeveloper 10g? 6-3

Exploring the JDeveloper Environment 6-4

Examining Workspaces 6-5

What Are Projects? 6-7

Creating JDeveloper Items 6-8

Creating an Application Workspace 6-9

Specifying Project Details 6-10

Selecting Additional Libraries 6-11

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Adding a New J2SE 6-12

Looking at the Directory Structure 6-13

Exploring the Skeleton Java Application 6-14

Finding Methods and Fields 6-15

Supporting Code Development with Profiler and Code Coach 6-16

Customizing JDeveloper 6-17

Using the Help System 6-18Obtaining Help on a Topic 6-19

Oracle JDeveloper 10g Debugger 6-20

Setting Breakpoints 6-22

Using the Debugger Windows 6-24

Stepping Through a Program 6-25

Watching Data and Variables 6-26

Summary 6-27


7 Creating Classes and Objects

Objectives 7-2Using Java Classes 7-4

Comparing Classes and Objects 7-5

Creating Objects 7-6

Using the newOperator 7-7

Comparing Primitives and Objects 7-8

Using the nul l Reference 7-9

Assigning References 7-10

Declaring Instance Variables 7-11

Accessing publ i c Instance Variables 7-12

Defining Methods 7-13Calling a Method 7-14

Specifying Method Arguments: Examples 7-15

Returning a Value from a Method 7-16

Calling Instance Methods 7-17

Applying Encapsulation in Java 7-18

Passing Primitives into Methods 7-19

Passing Object References into Methods 7-20

What Are Class Variables? 7-21

Initializing Class Variables 7-22

What Are Class Methods? 7-23

Guided Practice: Class Methods or Instance Methods 7-24

Examples in Java 7-25

Creating Classes Using the Class Editor 7-26

What Are Java Packages? 7-27

Grouping Classes in a Package 7-28

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Setting the CLASSPATHwith Packages 7-29

Access Modifiers 7-30

Summary 7-32


8 Object Life Cycle and Inner Classes

Objectives 8-2

Overloading Methods 8-4

Using the t hi s Reference 8-5

Initializing Instance Variables 8-6

What Are Constructors? 8-7

Defining and Overloading Constructors 8-8

Sharing Code Between Constructors 8-9

f i nal Variables, Methods, and Classes 8-10

Reclaiming Memory 8-11

Using the f i nal i ze( ) Method 8-12

What Are Inner Classes? 8-13

Using Member Inner Class 8-14Using Local Inner Class 8-15

Defining Anonymous Inner Classes 8-16

Using the Cal endar Class 8-17

Summary 8-18


9 Using Strings, String Buffer, Wrapper, and Text-Formatting Classes

Objectives 9-2

What Is a St r i ng? 9-3

Creating a St r i ng 9-4

Concatenating Strings 9-5

Performing Operations on Strings 9-6

Performing More Operations on Strings 9-7

Comparing St r i ng Objects 9-8

Producing Strings from Other Objects 9-9

Producing Strings from Primitives 9-10

Producing Primitives from Strings 9-11

Wrapper Class Conversion Methods 9-12

Changing the Contents of a String 9-13

Formatting Classes 9-14

Using the Si mpl eDat eFor mat Class 9-15Using the Mes sageFor mat Class 9-16

Using Deci mal For mat 9-17

Guided Practice 9-18

Using Regular Expressions 9-20

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About Syst em. out . pr i nt l n 9-23

About Out put St r eamand Pr i nt St r eam 9-24

What Is Object Serialization? 9-25

Serialization Streams, Interfaces, and Modifiers 9-28

Summary 9-29


10 Reusing Code with Inheritance and Polymorphism

Objectives 10-2

Key Object-Oriented Components 10-3

Example of Inheritance 10-4

Specifying Inheritance in Java 10-5

Defining Inheritance by Using Oracle JDeveloper 10g 10-6

What Does a Subclass Object Look Like? 10-7

Default Initialization 10-8

The super Reference 10-9

The super Reference Example 10-10

Using Superclass Constructors 10-11Specifying Additional Methods 10-13

Overriding Superclass Methods 10-15

Invoking Superclass Methods 10-17

Example of Polymorphism in Java 10-19

Treating a Subclass as Its Superclass 10-20

Browsing Superclass References by Using Oracle JDeveloper 10g 10-21

Acme Video and Polymorphism 10-22

Using Polymorphism for Acme Video 10-23

Using the i nst anceof Operator 10-25

Limiting Methods and Classes with f i nal 10-26Ensuring Genuine Inheritance 10-27

Summary 10-28

11 Using Arrays and Collections

Objectives 11-2

What Is an Array? 11-3

Creating an Array of Primitives 11-4

Declaring an Array of Primitives 11-5

Creating an Array Object for an Array of Primitives 11-6

Initializing Array Elements 11-8

Creating an Array of Obj ect References 11-9Initializing the Objects in the Array 11-10

Using an Array of Obj ect References 11-11

Arrays and Exceptions 11-12

Multidimensional Arrays 11-13

mai n( ) Revisited 11-14

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Working with Variable-Length Structures 11-15

Modifying a Vector 11-16

Accessing a Vector 11-17

Java Collections Framework 11-18

Collections Framework Components 11-20

Using Ar r ayLi st and Hasht abl e 11-21

Using I t er at or s 11-22Summary 11-23


12 Structuring Code by Using Abstract Classes and Interfaces

Objectives 12-2

Defining Abstract Classes 12-3

Creating Abstract Classes 12-4

What Are Abstract Methods? 12-5

Defining Abstract Methods 12-7

Defining and Using Interfaces 12-8

Examples of Interfaces 12-9Creating Interfaces 12-10

Implementing Interfaces 12-12

Sort: A Real-World Example 12-13

Overview of the Classes 12-14

How the Sort Works 12-15

The Sor t abl e Interface 12-16

The Sor t Class 12-17

The Movi e Class 12-18

Using the Sort 12-19

Using i nst anceof with Interfaces 12-20Summary 12-21


13 Throwing and Catching Exceptions

Objectives 13-2

What Is an Exception? 13-3

How Does Java Handle Exceptions? 13-4

Advantages of Java Exceptions: Separating Error Handling Code 13-5

Advantages of Java Exceptions: Passing Errors Up the Call Stack 13-7

Advantages of Java Exceptions: Exceptions Cannot Be Ignored 13-8

Checked Exceptions, Unchecked Exceptions, and Errors 13-9What to Do with an Exception 13-11

Catching and Handling Exceptions 13-12

Catching a Single Exception 13-13

Catching Multiple Exceptions 13-14

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Cleaning Up with a f i nal l y Block 13-15

Catching and Handling Exceptions: Guided Practice 13-16

Allowing an Exception to Pass to the Calling Method 13-18

Throwing Exceptions 13-19

Creating Exceptions 13-20

Catching an Exception and Throwing a Different Exception 13-21

Summary 13-22Practice 13: Overview 13-23

14 User Interface Design: Swing Basics Planning the Application Layout

Objectives 14-2

Running Java UI Applications 14-3

AWT, Swing, and JFC 14-4

Swing Features 14-6

Lightweight or Heavyweight Components? 14-8

Planning the UI Layout 14-9

The Containment Hierarchy 14-10

Top-Level Containers 14-12Intermediate Containers 14-14

Atomic Components 14-15

Layout Management Overview 14-16

Border Layout 14-18

GridBag Layout 14-19

GridBag Constraints 14-20

Using Layout Managers 14-22

Combining Layout Managers 14-24

Using Frames or Dialogs 14-25

Using J Panel Containers 14-27Adding Borders to Components 14-29

Using Internal Frames 14-30

Swing Text Controls 14-32

Adding Components with Oracle JDeveloper 10g 14-33

Creating a Frame 14-34

Adding Components 14-35

Setting Pluggable Look and Feel 14-37

Summary 14-39


15 Adding User Interface Components and Event HandlingObjectives 15-2

Swing Components 15-3

Swing Components in JDeveloper 15-5

Invoking the UI Editor 15-7

How to Add a Component to a Form 15-8

Edit the Properties of a Component 15-9

Code Generated by JDeveloper 15-10

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Mapping Database Types to Java Types 16-26

Handling an Unknown SQL Statement 16-28

Handling Exceptions 16-29

Managing Transactions 16-30

The Pr epar edSt at ement Object 16-31

How to Create a Pr epar edSt at ement 16-32

How to Execute a Pr epar edSt at ement 16-33Maximize Database Access 16-34

Connection Pooling 16-35

Summary 16-38


17 Deploying Appl ications by Using Java Web Start

Objectives 17-2

What Is Java Web Start? 17-3

Running a Web Start Application 17-4

Advantages of Web Start 17-5

Examining the JNLP File 17-6Deploying Applications with JDeveloper 17-7

Creating the Deployment Profile File 17-8

Saving the Deployment Profile 17-9

Selecting Files to Deploy 17-10

Making an Executable . j ar File 17-11

Creating and Deploying the Archive File 17-12

Using JDeveloper to Deploy an Application to Java Web Start 17-13

Step 1: Generate Deployment Profiles and Archive Application 17-14

Step 2a: Start OC4J 17-15

Step 2b: Creating a Connection 17-16

Step 3: Use Web Start Wizard to Create a JNLP File 17-17

Step 4: Archive and Deploy the Application to the OC4J Server 17-18

Summary 17-19


Appendix A: Practice Solu tions

Appendix B: Java Language Quick-Reference Guide

Appendix C: Order Ent ry Solut ion

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Preface


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Preface - 3

Profile

Prerequisites

Required: Previous experience with another 3GL programming language, preferably a structured

language such as Pascal or C

Suggested: Familiarity with basic HTML

How This Course Is Organized

Oracle 10g: Java Programming is an instructor-led course featuring lectures and hands-on exercises.

Online demonstrations and written practice sessions reinforce the concepts and skills introduced.


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Preface - 4

Related Publications

Oracle Publications

Title Part Number

Oracle 10g: Build J2EE Applications (inClass course) D17247GC10

Oracle JDeveloper 10g: Build Applications with Oracle ADF (inClass course) D16975GC10

Oracle JDeveloper Handbook (Oracle Press)

Additional Publications

System release bulletins

Installation and users guides

Read-me files

International Oracle Users Group (IOUG) articles

Oracle Magazine


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Preface - 5

Typographic Conventions

Typographic Conventions In Text

Convention Element Example

Bold Emphasized words and phrases

in Web content only

To navigate within this application, do not

click the Back and Forward buttons.

Bold italic Glossary terms (if there is a

glossary)

The algorithm inserts the new key.

Brackets Key names Press [Enter].

Caps and

lowercase

Buttons,

check boxes,

triggers,

windows

Click the Executable button.

Select the Registration Required check

box.

Assign a When-Validate-Item trigger.

Open the Master Schedule window.

Carets Menu paths Select File > Save.

Commas Key sequences Press and release these keys one at a

time:

[Alt], [F], [D]


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Preface - 6

Typographic Conventions (continued)

Typographic Conventions In Text (continued)

Convention Object or Term Example

Courier New,

case sensitive

Code output,

SQL and PL/SQL

code elements, Java

code elements,

directory names, file

names, passwords,

path names,

user input,

usernames

Code output: debug. set i ( I , 300) ;

SQL code elements: Use the SELECTcommand to view

information stored in the l ast _namecolumn of the emptable.

Java code elements: Java programming involves the

St r i ngand St r i ngBuf f er classes.

Directory names: bi n(DOS), $FMHOME(UNIX)

File names: Locate the i ni t . or afile.

Passwords: Use t i ger as your password.

Path names: Open c: \ my_docs\ pr oj ect s .

User input: Enter 300.

Usernames: Log on as scott .

Initial cap Graphics labels

(unless the term is a

proper noun)

Customer address (butOracle Payables)

Italic Emphasized words

and phrases in print

publications, titles

of books and

courses, variables

Do notsave changes to the database.

For further information, see Oracle7 Server SQL

Language Reference Manual.

Enter [email protected], where user_idisthe name of the user.

Plus signs Key combinations Press and hold these keys simultaneously:

[Control] + [Alt] + [Delete]

Quotation

marks

Lesson and chapter

titles in cross

references, interface

elements with long

names that have

only initial caps

This subject is covered in Unit II, Lesson 3, Working

with Objects.

Select the Include a reusable module component and

click Finish.

Use the WHEREclause of query property.


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Preface - 7

Typographic Conventions (continued)

Typographic Conventions in Navigation Paths

This course uses simplified navigation paths, such as the following example, to direct you through

Oracle Applications.

Example:

Invoice Batch Summary

(N) Invoice > Entry > Invoice Batches Summary (M) Query > Find (B) Approve

This simplified path translates to the following:

1. (N) From the Navigator window, select Invoice > Entry > Invoice Batches Summary.

2. (M) From the menu, select Query > Find.

3. (B) Click the Approve button.

Notation:

(N) = Navigator (I) = Icon(M) = Menu (H) = Hyperlink

(T) = Tab (B) = Button


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Introduction

Schedule: Timing Topic

10 minutes Lecture

10 minutes Total


21/329Oracle10g: Java Programming I-2

I-2 Copyright 2004, Oracle. All rights reserved.

Objectives

After completing this course, you should be able to dothe following:

Write stand-alone applications with the Java

programming language

Develop and deploy an application

Build, generate, and test application components

by using Oracle JDeveloper 10g


22/329Oracle10g: Java Programming I-3

I-3 Copyright 2004, Oracle. All rights reserved.

Course Overview

This course teaches you how to write Javaapplications.

You also learn how to bui ld, debug, and deploy

applications by using Oracle JDeveloper 10g.

The development environment is Oracle

JDeveloper 10g and the Oracle Database.

Instructor Note

The database used for this course is 9.2. It is the latest edition supported by the Development

Tools.


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Introducing the Java

and Oracle Platforms


60 minutes Lecture

00 minutes Practice

60 minutes Total


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Oracle10 : Java Pro rammin 1-2

1-2 Copyright 2004, Oracle. All rights reserved.

Objectives

After completing this lesson, you should be able to dothe following:

Identi fy the key elements of Java

Describe the Java Virtual Machine (JVM)

Examine how Java is used to build applications

Identi fy the key components of the J2SE Java

Development Kit (known as JDK or SDK)

Describe Java deployment options

Lesson Aim

This lesson introduces the background and usefulness of the Java language. It discusses Javas

position with the Oracle10g. Java is the programming language of choice for Internet

applications. It has gained this status because of its robust nature, the object-orientation of the

language, the depth of its predefined classes, and its write once, run anywhere deployment

model. You learn how Java supports object-oriented programming and architectural neutral

deployment.


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What Is Java?

Java: Is a platform and an object-oriented language

Was or iginally designed by Sun Microsystems for

consumer electronics

Contains a class library

Uses a virtual machine for program execution

What Is Java?

Designed by Sun Microsystems

Java is a platform and an object-oriented programming language, which was originallydeveloped by Sun Microsystems, Inc. It was created by James Gosling for use in consumerelectronics. Because of the robustness and platform-independent nature of the language, Javasoon moved beyond the consumer electronics industry and found a home on the World WideWeb. Java is a platform, which means that it is a complete development and deploymentenvironment.

Class LibrariesJava contains a broad set of predefined classes, which contain attributes and methods that handlemost of the fundamental requirements of programs. Window management, input/output, andnetwork communication classes are included in the Java Developers Kit (JDK). The classlibrary makes Java programming significantly easier and faster to develop when compared withother languages. JDK also contains several utilities to facilitate development processes. Theseutilities handle operations, such as debugging, deployment, and documentation.

Java Uses a Virtual Machine

One of the key elements of the Java language is platform independence. A Java program that iswritten on one platform can be deployed on any other platform. This is usually referred to as

write once, run anywhere (WORA). This task is accomplished through the use of the JavaVirtual Machine (JVM). JVM runs on a local machine and interprets the Java bytecode andconverts it into platform-specific machine code.


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Key Benefits of Java

Object-oriented Interpreted and platform-independent

Dynamic and distributed

Multithreaded

Robust and secure

Key Benefits of Java

Object-Oriented

An object is an entity that has data attributes, plus a set of functions that are used to manipulate

the object. Java is a strongly typed language, which means that almost everything in Java is an

object. The main exceptions are the primitive data types, such as integers and characters.

Interpreted and Platform Independent

Java programs are interpreted to the native machines instruction set at run time. Because Java

executes under the control of a JVM, Java programs can run on any operating system that

provides a JVM.

Dynamic and Distributed

Java classes can be downloaded dynamically over the network when required. In addition, Java

provides extensive support for client-server and distributed programming.


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Key Benefits of Java (continued)

Multithreaded

Java programs can contain multiple threads to carry out many tasks in parallel. Multithreading

capability is built into Java and is under the control of the platform-dependent JVM.

Robust and Secure

Java has built-in capabilities to prevent memory corruption. Java automatically manages the

processes of memory allocation and array bounds checking. It prohibits pointer arithmetic, and

restricts objects to named spaces in memory.

Instructor Note

Historically speaking, Goslings team started using C++ initially, but soon found that C++programs were too liable to crash, partly due to language complexity, and also because of thedestructive capabilities of C++ constructs, such as pointers. To overcome these problems,Goslings team invented their own object-oriented language, called Oak. To make it robust, theyeliminated problematic language constructs, and made it architecturally neutral, by fullyspecifying the semantics of the language and creating a virtual machine to execute the programs.Oak was designed from the ground up to look like C++ but also to reduce the learning curve forthose who knew C++. Oak was renamed Java, when it gained popularity in the World Wide Weband the revolution began. The robustness, compactness, platform independence, and flexibilitythat had been designed for the electronics consumer market make Java the ideal language forcreating Web-based programs. Because Java is an interpreted language, it is slower than C++ interms of execution speed, but this is often unimportant when dealing with user interactions.


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An Object-Oriented Approach

Objects and classes An object is a run-time representation of a thing.

A c lass is a static definit ion of things.

Class models elaborate:

Existing classes and objects

Behavior, purpose, and structure

Relationships between classes

Relationships between run-time objects Same models exist throughout the project.

Analysis ImplementationIntegrationand testing

Design

CLASS MODELS

An Object-Oriented Approach

Object-oriented programming is a powerful and natural paradigm that is used to write

application programs. The approach ensures that programs survive the changes accompanying

the growth of a business and its systems. After you understand the function of each object and

develop clean, reliable interfaces between the functions, you can decommission older parts of an

application system without concern.

Classes provide a means to capture the structure and behavior of a real-world person, place, or

thing, and represent a one-to-one mapping between the real-world object and its implementation.

This one-to-one mapping tends to eliminate the typical transformations that are found innonobject-oriented design approaches.


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Platform Independence

Java source code is stored as text in a .java file. The .java file is compiled into .class files.

A .class file contains Java bytecodes

(instructions).

The bytecodes are interpreted at run t ime.

The Java .class file is the executable code.

Compile

Movie.java

JVM

Running programMovie.class

(javac) (java)

Platform Independence

Java Is an Interpreted Language

Java program source code is stored in . j ava files. For example, a Java program dealing withmovies in a video rental company may have files calledMovi e. j ava, Cust omer . j ava, andRent al . j ava.

Each . j ava file is compiled into a corresponding . cl ass file with the same name. Forexample, a Movi e. j ava compiles to at least one class file. (Inner classes is quite common.)But, the public Movi e. j ava compiles to one Movi e. cl ass. These. cl ass files contain

Java bytecodes, which are platform-independent machine instructions.Java Virtual Machine (JVM)

JVM provides the environment for running Java programs. The JVM interprets Java bytecodesinto the native instruction set for the machine on which the program is currently running.

The same . cl ass files can be executed unaltered on any platform for which a JVM is provided.For this reason, JVM is sometimes referred to as a virtual processor.

Traditional Compiled Languages

When compiling a traditional language such as C, the code written by the programmer isconverted into machine instructions for the platform on which the compilation takes place. This

compiled program can then run only on machines that have the same processor as that on whichit was compiled, such as Intel, SPARC, or Alpha.


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Using Java with Enterprise

Internet Computing

Web

server

Application

server

PresentationBusiness

logic

Servlets

JavaServer

Pages (JSPs)

Enterprise

JavaBeans (EJB)

CORBA

Client Data

Java and Enterprise Internet Computing

You can design Java programs as server-based components that form scalable Internet

applications.

The currently accepted model for Java Internet computing divides the end-to-end application

process into several logical tiers. To utilize this model, JavaSoft defined the Java2, Enterprise

Edition (J2EE). There are four logical tiers:

Client Tier

When Java is needed to execute on client machines, it is typically implemented as a browser-

based application. But a thin client can be just Web pages that are delivered from a server as

HTML.

Presentation Tier

This is executed on a Web server. Code in this tier handles the applications presentation to the

client. Common Java features for this function are servlets and JavaServer Pages (JSPs). Servlets

and JSPs can each generate dynamic HTML for display as Web pages to clients.


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Java and Enterprise Internet Computing (continued)

Application (Business Logic) Tier

You can use Java on an application server to implement shareable, reusable business logic as

application components. A common way to implement this is to use component models, such as

Enterprise JavaBeans (EJB) and Common Object Request Broker Architecture (CORBA)

objects. These two components are also to be considered during design time, when a distributed

environment is required.

Data Tier

The data server not only stores data, but can also store and execute Java code, particularly where

this code is data intensive or enforces validation rules pertaining to the data. You can also use

Business Components, from Oracles Application Development Framework (ADF), to support

the data access of your application.


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Using the Java Virtual Machine

Operating system

JVM

Applicat ion

Running Java Applications

All Java applications run within a Java Virtual Machine (JVM). JVM is invoked differently

depending on whether the Java program is an application or an applet.

Applications

You can run stand-alone applications by invoking a local JVM directly from the operating

system command line and supplying the name of the main class for the application. After loading

the applications main class file, JVM runs the program by calling a known entry point in theclass; that is, a public static method called mai n( . . . ) . JVM runs the code by interpreting the

bytecodes in the Java program and converting bytecode into platform-specific machineinstructions.


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Running Java Applications (continued)

Running Java Applets

A Java applet is a special type of Java program that is used in Web pages. When a Web browser

reads an HTML page with an applet tag, it downloads the applet over the network to the local

system and runs the applet in a JVM that is built into the browser. The browser invokes a

specific call sequence of known methods in the Java applet class to execute the Java code in the

context of the browsers JVM. The applet entry points differ from the entry point that is used by

JVM to run stand-alone applications.

In the case of an applet, the presentation server is not necessarily used. A Java application is

quite capable, and typically is configured, to connect directly to the business logic.

Applets are not covered in this course, and are only presented here for completeness. In this

course, during deployment of your application, you use the Java Web Start product.


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How Does JVM Work?

The class loader loads all required classes. JVM uses a CLASSPATH setting to locate class f iles.

JVM Verif ier checks for i llegal bytecodes.

JVM Verifier executes bytecodes.

JVM may invoke a Just-In-Time (JIT) compiler.

Memory Manager releases memory used by the

dereferenced object back to the OS.

JVM handles Garbage col lection.

How Does JVM Work?

JVM Class Loader

When a . cl ass file is run, it may require other classes to help perform its task. These classes

are loaded automatically by the class loader in JVM. The required classes may reside on thelocal disk or on another system across the network. JVM uses theCLASSPATHenvironmentvariable to determine the location of local . cl ass files. The classpath can be added in run timeby using thej ava - cp or - cl asspat h option.

Classes that are loaded from the network are kept in a separate namespace from those on the

local system. This prevents name clashes and the replacement or overriding of standard classes,malicious or otherwise.

JVM Verifier

It is the job of the verifier to make sure that the Java code that is being interpreted does not

violate any of the basic rules of the Java language and that the code is from a trusted source. A

trusted source is an option; and if used, the check is not performed.

This validation ensures that there are no memory access violations or other illegal actions

performed.


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How Does JVM Work? (continued)

Bytecode Interpreter

JVM is the bytecode interpreter that executes the bytecodes for the loaded class. If enabled, JVM

can use just-in-time (JIT) technology to translate Java bytecodes into native machine

instructions.

Memory Management

JVM keeps track of all instances in use. After an instance is no longer in use, JVM is allowed to

release the memory that is used by that object. It performs the release of memory after the object

is no longer needed, but not necessarily immediately. The process (thread) that JVM uses to

manage dereferenced objects is called garbage collection.


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Benefits of Just-In-Time (JIT) Compilers

JIT compilers: Improve performance

Are useful if the same bytecodes are executed

repeatedly

Translate bytecodes to native instruction

Optimize repetitive code, such as loops

Use Java HotSpot VM for better performance and

reliability

Just-In-Time (JIT) Compilers

JVMs translate Java bytecodes into native machine instructions. What happens if the same code

is executed again, later in the program? In an environment without JIT compilers, the code is

interpreted every time it is encountered, even if it has already been interpreted earlier in the

program.

The compilers are designed to easily translate bytecode into machine code, which is optimized to

run on the target platform.

Benefits of Just-In-Time Compilers

Most JVMs now support JIT compilation. JIT compilers translate bytecodes only the first time

that they are encountered; if the same code is executed later, then it is automatically mapped to

the corresponding native machine instruction.

JIT compilers enable Java programs to run more quickly because they obviate the need for

repeated translation of bytecodes to native machine instructions. This is especially effective in

repetitive code, such as loops or recursive functions. Some JIT compilers are intelligent enough

to optimize groups of related bytecodes into more efficient native machine instructions.


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Just-In-Time (JIT) Compilers (continued)

Java HotSpot

The Java HotSpot virtual machine (VM) is a key component in maximizing the deployment of

enterprise applications. It is a core component of Java 2, Standard Edition (J2SE) software,

which is supported by leading application vendors and technologies. Java HotSpot VM supports

virtually all aspects of development, deployment, and management of corporate applications.


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Implementing Security

in the Java Environment

Interface-specific access

Class loader

Bytecode verifier

Language and compiler

Java Security Layers

Language and Compiler

The Java language was designed to be a safe language. The constructs that allow direct

manipulation of memory pointers have been eliminated, thereby reducing or even eliminating

run-time program crashes and, as a consequence, memory leaks.

Class Loader

The class loader ensures that each class coming from a local source (built-ins) and the classes

from each network source are stored separately. During execution, the run-time system first

looks up the built-ins for referenced classes; if they are not found, then it consults the referencing

class. This ensures that built-in classes are not overridden by network-loaded classes. This

prevents spoofing, or overriding the expected and trusted behavior of a built-in class. Inside a

JVM, there can be several classloaders controlling each applications namespace.


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Java Security Layers (continued)

Bytecode Verifier

During the execution of a Java program, JVM can import code from anywhere. Java must make

sure that the imported code is from a trustworthy source. To accomplish this task, the run-time

system performs a series of checks called bytecode verification.

Interface-Specific Access

Built-in classes and methods control access to the local file system and network resources. Theseclasses are restrictive by default. If imported code tries to access the local file system, then the

security mechanism prompts the user.


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Deployment of Java Applications

Client-side deployment: JVM runs stand-alone applications from the

command line.

Classes load from a local disk, eliminating the need

to load classes over a network.

Server-side deployment:

Serves multiple clients from a single source

Is compatible with a multit ier model for Internet

computing.

Java Applications

Java originally gained popular acceptance because of the success of its applets. Today, however,

it is also possible to write stand-alone applications in Java. A Java application is invoked by

using a JVM and is not run from within a browser.

Client-Side Deployment

Java applications can be deployed to run stand-alone applications within a local operating

system, from the command line. For example, Java applications can access the local file system

or establish connections with other machines on the network.

Server-Side Deployment

Java applications can also execute on the server machine, as long as a JVM is available on that

platform. The use of server-side Java applications is compatible with the multitier model for

Internet computing.


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Using Java with Oracle 10g

Oracle

database

Web

serverClient

Application

server

PresentationBusiness

logic

Data

OracleApplicat ion Server

Java and Oracle 10g

Oracle 10g is a complete and integrated platform, which supports all the server-side

requirements for Java applications. Oracle 10g comprises the following:

Oracle Database 10g

In addition to its database management features, the Oracle Database (currently, version 10g)

provides support for a variety of Java-based structures including Java components and Java

stored procedures. These Java structures are executed in the database by its built-in Java Virtual

Machine, called the Enterprise Java Engine (EJE).

Oracle Application Server 10g

The Oracle Application Server 10g maintains and executes all your application logic, including

Enterprise JavaBeans, through its own built-in JVM. Oracle Application Server 10g uses the

OC4J J2EE server to execute servlets and JSPs. Oracle Application Server 10g Enterprise

Manager is the tool that is used to manage and distribute applications, for ease of use.

Instructor Note

For more architectural information about Oracle Application Server 10g, direct students to thevarious eClasses that are available on the Oracle Learning Network.


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Java Software Development Kit

Sun Java J2SE (known as JDK and Java SDK)provides:

Compiler (javac)

Core class library

classes.zip

rt.jar

Debugger (jdb)

Bytecode interpreter: The JVM (java) Documentation generator (javadoc)

Java Archive utility (jar)

Others

J2SE

Java Software Development Kit

Sun provides the Java 2, Standard Edition (J2SE), which is also known as Java Software

Development Kit (Java SDK) or the Java Development Kit (JDK). The components that are

provided by the J2SE include the following:

The Java compiler is javac. It compiles Java source code into Java bytecodes.

The Java bytecode interpreter, java, is the engine that runs Java applications.

The program that generates documentation in HTML from Java source code comments is

javadoc.

Core Class LibraryThe J2SE provides core Java class in the following class library files:

cl asses. zi p located in the jdk_home\ l i b for JDK 1.1.x or earlier r t . j ar located in the jdk_home\ j r e\ l i b for Java SDK 1.2.x or later

Other Java J2SE Tools j db is the Java class debugger. It is similar to the dbx or gdb debuggers on UNIX. j ar is used to create Java Archive (JAR) files, which are zipped Java programs. j avah is used to generate C files for native methods. j avakey supports the generation of certification keys for trusted Java code.

j avap is used to disassemble Java bytecodes into human-readable format. nat i ve2asci i converts Java source code to Latin 1 characters. ser i al ver is used to generate version numbers for classes.


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Using the Appropriate Development Kit

Java2 comes in three sizes: J2ME (Micro Edition): Version specifically targeted

at the consumer space

J2SE (Standard Edition): Complete ground-up

development environment for the Internet

J2EE (Enterprise Edition): Everything in the J2SE

plus an application server and prototyping tools

A Size for Every Need

Java 2, Micro Edition

The technology that Java 2, Micro Edition (J2ME) uses covers the range of extremely tiny

commodities, such as smart cards or a pager, all the way up to the set-top box, which is an

appliance that is almost as powerful as a computer. Like the other editions, the J2ME platform

maintains the qualities for which Java technology has become famous.

Java 2, Standard Edition

The J2SE technology has revolutionized computing with the introduction of a stable, secure, and

feature-complete development and deployment environment that is designed from the ground up

for the Web. It provides cross-platform compatibility, safe network delivery, and smart card to

supercomputer scalability. It provides software developers with a platform for rapid application

development.

Java 2, Enterprise Edition

The J2EE platform is intended as a proof of concept, and a guide for implementations in the

application server marketplace. The J2EE SDK includes a J2EE application server and various

tools to help developers prototype J2EE applications.


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Integrated Development Environment

Development

UML

ADF

XML

SCM

Debug

Exchange

Database

HTML

Deployment

Synchronized changes

Integrated Development Environment

The add-in API architecture of Integrated Development Environment (IDE) means that all the

tool components (for example, navigator, editor, and modeller) share memory models and event

systems. In this way, an update in one tool is notified to another tool so that it can refresh its

image or take other appropriate actions.

In Oracle 10g, the JDeveloper IDE was developed in pure Java. Synchronization between model

and code can be set so that you can decide to work by using one or the other user interface.

Customizable Environment

You can customize the JDeveloper Integrated Development Environment and arrange its look to

better suit your project needs and programming style. To suit the IDE to your individual taste,

you can:

Change the look and feel of the IDE

Create and manipulate custom navigators

Customize the Component Palette

Customize the IDE environment

Select JDevelopers embedded J2EE server

Arrange the windows in the IDE


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Exploring the JDeveloper Environment

System Navigator Code Editor Property Inspector

Component Palette

The Oracle JDeveloper 10g Environment

JDeveloper contains four major user interface components. These components are what you use

to edit code, design and manage the user interface, and navigate around your program.

Component Palette

Properties are attributes that define how a component appears and responds at run time. In

JDeveloper, you set a components initial properties during design time, and your code can

change those properties at run time.

System Navigator

System Navigator is made up of two components. The Navigator pane shows a list of files orclasses in a project. The files may be Java source files, . cl ass files, graphics files, HTML,

XML documents, and so on. The Structure pane lists all the methods, fields, and graphical user

interface (GUI) components in a selected class.

Code Editor

Editors are where most of the work takes place; this is where you write code and design user

interfaces. Open an editor by double-clicking the item you want to edit or view.

Property Inspector

Property Inspector is the window that shows the properties and events associated with a selected

component in the design region of a viewer.


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Oracle10g Products

Oracle 10g Products

Oracle Database 10g

The Oracle Database manages all your information: Word documents, Excel spreadsheets, XML,

images, and so on. Oracle Development Suite 10g tools can automatically reuse the database

structure and its integrity constraints, which reduces the amount of manual coding.

Oracle Application Server 10g

The Oracle Application Server 10g runs all your applications: J2EE applications, Forms,

wireless, portals, and business intelligence. Using Oracle Application Server 10g, all applications

that are developed with Oracle Development Suite 10g can be deployed and managed in a single

application server.

Oracle Developer Suite 10g

Oracle Developer Suite 10g leverages the infrastructure that is offered by Oracle Application

Server 10g and Oracle Database 10g enabling developers to build scalable, secure, and reliable

e-business applications quickly and easily. The suite provides a complete and highly productive

development environment for building applications. Oracle JDeveloper 10g is now available as a

separate product and not just as part of the developer suite product.


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Summary

In th is lesson, you should have learned the following: Java code is compiled into platform-independent

bytecodes.

Bytecodes are interpreted by JVM.

Java appl ications can be stand-alone or

implemented across an Internet-computing model.


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Defining Object-Oriented Principles


60 minutes Lecture

20 minutes Practice

80 minutes Total


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Objectives

After completing this lesson, you should be able to dothe following:

Define objects and explain how they are used

Associate objects so that they can communicate

and interact via messages

Define classes and explain how they are used

Describe object-oriented (OO) principles: c lasses,

objects, and methods Describe the value of Reusable Software

Components

Examine the OO model that is used in this course

Lesson Aim

This lesson introduces the concepts of classes and objects, which are the foundation to the

object-oriented approach to building applications. It explains the benefits and implementation of

object-oriented principles. It introduces Classes, Objects, and Methods and contrasts OO

principles with traditional programming techniques. This lesson defines the terms Abstraction,

Encapsulation, Inheritance, and Polymorphism, and explains the benefits of each of these

principles. The course application class structure is presented and a simple use case scenario is

discussed to provide context for using an object defined by the class model.


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Overview of Object-Oriented Programming

Object-oriented programming (OOP) is a relatively new paradigm for creating computer

programs that are adaptable, reusable, and can stand the test of time. The functionality comes

from the design of discrete classes that contain information about objects as well as expected

behaviors. In an OO program, objects send messages to one another and expect certain behaviors

or messages in return.

A good example of object orientation is the personal computer (PC). Although this is not a

programming example, it serves as an example of what OOP can deliver in a programmingenvironment.

Each PC is made up of components that are manufactured by several unrelated companies. Each

component is built to a specification that includes information and behaviors. A CD drive, for

example, is expected to return data from a CD when the operating system asks for it. The PC

manufacturer does not need to be concerned with the internal workings of the CD drive, only that

it responds to requests appropriately.

In the same way, an OO program may make calls to objects without knowing all the details of

the objects. The program simply expects to get information or produce a specific behavior. By

defining each of these objects separately, the internal workings of each object can change as longas the way they are called and how they behave stay the same.

OOP uses a number of techniques to achieve adaptability including abstraction, encapsulation,

inheritance, and polymorphism. Each of these topics is discussed in the next few pages.


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What Is Modeling?

Models perform the following funct ions: Descr ibe exactly what the business needs

Facilitate discussion

Prevent mistakes

Modeling and implementation are treated

separately.

Before coding can begin, the model must be

correct.

The House-Building Metaphor

Imagine someone who wants to have a house built. Initially, the house exists only in the minds of

the future home owners as ideas, or pieces of various dreams. Sometimes, the future inhabitants

may not even know what they want, or know whether what they want is even feasible. Dreams

may be full of internal contradictions and impossibilities. This is not a problem in the dream

world; in the physical realm, any inconsistencies and obstacles must be resolved before someone

can construct the house.

A building contractor needs a solid set of blueprints of the house with a description of the

materials to be used, the size of the roof beams, the capacity of the plumbing, and so on. Thecontractor follows the plan, and has the knowledge to construct what is on the blueprint. But how

do the ideas of the home owner become the blueprint for the contractor? This is where the

architect comes in.

The architect is the intermediary between the sponsor and the contractor. He or she is trained in

the skills of translating ideas into models. The architects skills in extracting ideas, putting them

down in a format that enables discussion and analysis, giving advice, describing sensible options,

documenting them, and confirming them with the home owners, are the cornerstones to

providing the future home owners with a plan of the home they want.


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What Are Classes and Objects?

A class: Models an abstraction of objects

Defines the attributes and behaviors of

objects

Is the blueprint that defines an object

An object:

Is stamped out of the class mold

Is a single instance of a class Retains the structure and behavior

of a class

What Is an Object?

An object is something tangible, something that can be seen or touched, or something

that can be alluded to and thought about.

Object-oriented programs consist of several objects. These objects communicate with each other

by sending messages from one object to another. In a true object-oriented program, that is all you

have: a coherent group of communicating objects. New objects are created when needed, old

ones are deleted, and existing objects carry out operations by sending messages.

Some examples of objects in an OO program are Customer, Invoice, RentalAgreement, Video,

and so on. Each of these objects holds information about itself and performs certain behaviors. Acustomer has a name, address, and phone number. A customer may also rent a video, return a

video, pay a bill, and have other behaviors.

What Are Classes?

A class is a model of abstraction from real-world objects. A class defines the properties and

behavior of a set of objects. A class denotes a category of objects and acts as a blueprint for

creating that type of object.


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An Objects Attributes Maintain Its State

Objects have knowledge about their current state. Each piece of knowledge is called an attribute.

The values of attributes dictate the objects state.

Att ribute: Ink amount

At tr ibute: Cash available

Object: My blue pen

Object: Acme Bank ATM

An Object s Attr ibutes Maintain Its State

All the data that an OO system requires must be located in attributes of the existing objects.

Some objects have little or no data, whereas other objects have a lot of data; it depends entirely

on the operations that the object is to perform.

The collection attributes that are defined in an object determine its internal structure; in essence,

the object is a composite data structure, which is often called a user-defined type.

The values that are held in the attributes, at a given point in time, represent thecurrent state of

the object. As the values of attributes change, over time, the state of the object changes. The state

of an object is remembered as long as the object exists in the system (memory). The attributevalues are typically altered by executing an object method in response to some internal or

external event. It is the job of the object code to maintain the integrity of the objects state; that

is, to ensure that the object state is valid for that object.


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An Object s Attr ibutes Maintain Its State (cont inued)

Typical Attributes

As with operations, different objects store different attributes. For example, the Acme BankATMobject has attributes such as cash available, cards recognized, ATM code, and so on. Thebl ue pen object has attributes such as amount of ink remaining, diameter of nib, length of

stem, and so on.

Attributes are often deduced after you have decided what operations the object will supply. After

you know what the object must do, you are much better positioned to decide what attributes the

object must store to support these operations. Often, the attributes of an object are initially

known and can be used to define the type of operations that are required to maintain their value.


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Objects Have Behavior

An object exists to provide behavior (functionality)to the system.

Each distinct behavior is called an operation.

Operation: Write

Operation: Withdraw

Object: My blue pen

Object: Acme Bank ATM

Objects Have Behavior

The major purpose that is served by objects is performing operations in the system in which theyexist. Object technology decomposes a system entirely into objects; all the interactions betweenthe system and the outside world, and all the internal computations of the system, are carried outby the operations (or methods) of objects.

Typical Operations

Different objects naturally perform different operations. For example, theAcme Bank ATMobject has operations such as withdraw, print receipt, swipe card, and so on. Alternatively, the

my bl ue pen object has operations such as write, leak ink, and so on.For each object, you have to ask yourself: What does this object do for me? In other words,what services does this object supply for the other objects in the system? To do this, you musthave an idea about how the object will be used in the system; otherwise, you may end updefining several operations for each object, which is clearly unsatisfactory. It is important tounderstand how the object will be used in the system and to specify only the operations that arerelevant for that mode of usage.

You must also ask how the state of the object is changed; that is, How do the values that areheld in the object attribute get modified? This question enables you to define operations tomaintain the internal details of an object.


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Objects Are Modeled as Abstractions

A Java object is modeled as an abstractrepresentation of a real-world object.

Model only those attributes and operations that

are relevant to the context of the problem.

Real-world attributes/operations that you may not want to model:

At tr ibutes: Ink color

Operations: Refill , change color, point, write

Context: Product catalog

Real-world attributes/operations that you may want to model:

At tributes: Model, manufacturer, pr ice

Operations: Change price

Objects Are Modeled as Abstractions

How do you decide what operations and attributes are relevant to the model of themy bl uepen object? The answer is simple. You must understand how the object will be used by the other

objects in the context of this particular system. You model the object as an abstraction of the

real-world example in the context in which it exists.

For example, in the context of a product catalog, the relevant attributes of a pen are reported,such as the model or name, price, and the manufacturer (for example, Mont Blanc). Theoperations that are relevant to this catalog would be to change the price of this pen.

You may need to know whether the pen can be used to write text, be refilled, or have its inkcolor changed by replacing a cartridge. However, these latter operations are more relevant to theway the pen is used by the customer who is purchasing the pen, and therefore the refill, write,

change ink operations are not relevant to the catalog application context and must not bemodeled. When deciding on the attributes and operations for an object, always ask whether theyhave relevance in the domain of the application; always evaluate the attributes and operations inthe application context; that is, Are they required to successfully implement the system to meetbusiness requirements?


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Objects Are Modeled as Abstractions (continued)

Every Object Is Unique

By definition, each object instance has a unique identity; even if two or more objects haveidentical states, that is, if their attribute values are the same, the system always treats them asdifferent objects. When you create objects in software, you are given ahandle to the object,called an object reference in the Java language. In Java, this handle or object reference is given aname by which it can refer to the object.


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A PC may be

an object.

A PC may have a

CD drive, which

may be an object.

A PC may have a

keyboard, mouse, and

network card, all of which

may be objects.

Defining Object Composition

Objects can be composed of other objects. Objects can be part of other objects.

This relationship between objects is known as

aggregation.

Defining Object Composition

For example, when you talk about writing or reading from a CD drive, you consider the CD

drive as a single object. You may also discuss how the CD drive interacts with the personal

computer system; you treat the computer systems as a single object as well.

When an engineer is called in to repair a CD drive problem, his or her perspective of a CD drive

is more detailed. The engineer visualizes the CD drive spindle, the drive tray, and the laser beam

or reader.

Each of these are components of the CD drive object, and are objects in their own right. Each of

these views of the CD drive is equally valid, and each can be expressed at different times.

When discussing objects, it is useful to use as high a level of abstraction as possible. In this way,

you can conceptualize more of the important objects, and understand more about how the system

works.


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Defining Object Composition (continued)

Aggregation

This concept of objects being composed of many subobjects is known as aggregation.

When you break a big object down into several low-level objects, these low-level objects can

often be reused in subsequent projects. For example, ATMs use keypads, but so do cash

registers, telephones, and television remote controls.

Note: An aggregation is a special type (closely coupled) of association known as acomposition.

To make a distinction, think of an association as a collaborates with relationship. Think of an

aggregation as a made of or composed of relationshipfor example, an account is made of

transactions, whereas an order is made of order lines. There are two types of aggregation, strong

and weak. Strong aggregation is also called composition. Both are implemented by using

references in Java.


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The Donut Diagram

getAge()

Client or

sender

Person

Messagename

address

birthdate

getName

setBirthdate getAge

getAddress setAddress

The Donut Diagram

The donut diagram provides a visible reminder that an object presents an external interface in

the form of methods and that its instance variables (in this case, name, address, and birthdate) are

private and hidden inside.

Client objects interact with this Per son object by sending messages to it; that is, by invokingits public methods. The client does not know how theget Age method works, nor should the

client care. There could be an age variable in the place of the calculation based on the birthdate

variable. Or perhaps this kind of object returns a constant 39.

Note: This style of diagram has been a very popular one that is useful for conveying concepts.However, for real-world projects, it quickly becomes limiting: Real objects could have many

methods, which would not fit very well. A similar diagram, which ispart of Unified Modeling

Language (UML), is known as an interaction diagram. An interaction diagram is a generic term

that applies to several types of diagrams, such as collaboration diagrams, activity diagrams, and

sequence diagrams. They all represent in different ways where objects are drawn simply as

circles, and messages among them are drawn as arrows.

Oracle University provides an inClass course on UML techniques and notation namedObject-

Oriented Analysis and Design using the Unified Modeling Language (UML).

For further information, refer to http://education.oracle.com.


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Guided Practice:

Spot the Operations and Attributes

Spot the Operations and Attributes

For each graphic, specify at least three attributes and three operations.

Objects Operations Attributes

My pencil Write, erase Lead color

My pen Write, refill Ink color, ink amount

Jaws Eat, swim Capacity, speed

Car

Truck

Satellite


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Collaborating Objects

Collaborating objects work together to complete a taskand form the basis of an application system.

All methods are defined within a class and are not

defined globally as in traditional languages.

All objects are created from classes and contain

all the attributes and methods of that class.

Objects must associate with each other to

collaborate on common tasks. Associated objects communicate by sending

messages.

A System Is a Col lect ion of Col laborat ing Objects

An object system is made up of a collection of different types of objects. If the system is

organized to perform some task, then it must ensure that appropriate objects collaborate with

each other to complete the task. In an object-oriented application, collaboration is necessary

because all code and data are held in some class or object; there is no concept of global methods

or variables.

Objects must first be associated with each other before they can collaborate. After objects are

associated, communication is done by one object sending a message to another object; that is, the

sending object must know the recipient of the message. A message is a request to perform part ofthe functionality that is required to support the task.

The association between objects is achieved dynamically through areference. (That is, two

classes may associate with each other, and two objects may have a link between them.) A

reference forms a link or simply a relationship between the objects. In programming terms, a

reference can be implemented in various ways. For example, a variable in one object contains areference to the other object. In Java, one way to create an object is to use thenewoperator.

Movi e m1 = new Movi e( )

In this example, the class definition is called Movi e that is used as a data type for the variablem1. The variable m1 is defined to hold a reference to the new movie object. Another example of

a link between collaborating objects may be: The customer is the owner of the account, and the

account is owned by the customer.


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Objects Interact Through Messages

Objects communicate by sending messages.

A sending object must be associated with orlinked to the receiving object.

The message sender requests the receiver toperform the operation that is named in themessage.

This communication is similar to calling aprocedure:

The sender calls a method of the receiver.

The receiver executes the called method. Calling a method is always in the context of a

particular object:myPen.write( ): Object-oriented programming

write (myPen): Traditional structuredprogramming

Objects Interact Through Messages

Methods are named blocks of code similar to procedures or functions. The OO terminology

sending a message indicates that an object communicates with another object by requesting a

behavior and the associated object is invoked. Before one object can send a message to another,

the sender must be linked, or associated, with the receiver, via an object reference. Therefore,

when a message is sent to a receiver, it executes a method in response.

The receiver responsible for executing the method must have an interface matching the behaviorthat is requested in the message to carry out a particular task or algorithm.

The process of message-sending is analogous to calling a procedure in a traditional language.The sender transfers control to the receiver and resumes execution when the receiver returns

control. One key difference is that when you call a procedure, the call is bound to a specific

piece of code (some subroutine). For example, using the Pen example in the slide:Pen myPen = new Pen( ) ; / / get r ef erence t o a pen obj ectmyPen. wr i t e( ) ; / / Send wr i t e( ) message t o myPen

When you send a message, the specific piece of code that gets executeddepends on the class (thetype) of the receiver object. This is required to enable the principle ofpolymorphism, to exist.

Remember, you send a message to an object. This notion of a targeted recipient is different from

calling a procedure.


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When you create my blue pen, you do not have to

specify its operations or attributes. You simply

say what class it belongs to.

What Is a Class?

A class is a template for objects. A class definition specifies the operations and

attributes for all instances of that class.

A class is used to manage complexity.

A Class Is a Template for All Objects of That Type

In an object-oriented application, a class is a specification of all the operations and attributes for

that type of object. When you create a particular object (or instance) of that class, you must

initialize the attributes and links with specific values. This can be done either when you create

the object or at a later stage by carrying out some operation on the object.

If you view a class definition as a cookie-cutter, then each class creates cookies (objects) of thesame shape (set of operations, attributes, and links).

Examples of Classes and Objects

To describe the characteristics of all pens, you may define a pen class and specify operations,such as write and refill, and attributes, such as ink color and ink remaining. You can then createindividual pen objects to represent my blue pen, teachers red pen, and so on.

When you create a pen object, you may initialize the ink amount to be full (or empty) andspecify the color of the ink. The write operation for the pen would presumably check the value ofink amount and refuse to write if the pen was empty.

Classes Are a Natural Way of Describing Similar Objects

The concept of classes is something that you use every day, without realizing it. For example,when you sat down in this classroom, presumably you sat on a chair. You probably did not carewhich particular chair object you used, as long as the object exhibited all the structure and

behavior of an object belonging to the chair class. The use of chair objects comes naturally toyou after you have grasped the concept of chair, because all chairs exhibit the same propertiesalthough they may each have differing attributes.


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How Do You Identify a Class?

Identify the common behavior and structure for agroup of objects.

Recognize a single coherent concept.

Caution: A common misconception is the use of

the words classes and objects interchangeably.

Classes define objects.

My blue pen ops: write, refill

attr ibs: ink amount, color of ink

Your blue pen ops: write, refill

attribs: ink amount

How Do You Classify Objects?

The dictionary defines a class as a set, collection, group, or configuration containing members

having or thought to have at least one attribute in common.

Most objects in the real world do not have names; you usually identify them by the class that

they belong to. For example, the large woody leafy thing at the bottom of your garden is usually

referred to as a tree. The object is the thing at the bottom of your garden, but the class it belongs

to is tree.

Object-oriented software development is all about identifying classes and defining what you

mean by them; that is, Which of all its possible operations, attributes, and links are youinterested in for our system?

It is not always as easy as spotting the trees from the woods; sometimes you get many objects

that do not seem to have much in common, and you have to work at identifying the similarities

between the objects.

Classification Is Not Just a Computer Science Concept

Classification is not a new computer science technique; classification has been going on since

the time of Plato. Most of the objects in the real world are referred to by using a classification

system, and you often use different classifications for the same objects depending on yourcurrent viewpoint.


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Comparing Classes and Objects

Classes are static definit ions that you can use tounderstand all the objects of that class.

Objects are the dynamic entities that exist in the

real world and your simulation of it .

Caution: OO people almost always use the words

classes and objects interchangeably; you must

understand the context to dif ferentiate between

the two meanings.

Comparing Classes and Objects

Objects exist only at run time; they hold attribute values, provide operations to be executed, and

communicate by sending messages to each other. There can be many instances of a particular

type of object.

Classes are loaded into the run-time environment and used as a template to create the object

instances, similar to a cookie-cutter. Although they are static definitions, they must be available

at run time to be able to manufacture objects with all the qualities (for example, structure and

function) defined in the class.

A loose analogy from a purely structural perspective: A database table is a definition of a row;that is, the table structure can be loosely thought of as a class definition, and each row holds

specific values as a separate instance with a structure that is defined by the table (the class). Both

the table definition and its rows must exist in the database. There are many rows, but only one

table definition.


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Comparing Classes and Objects (continued)

How Many Objects of a Particular Class Exist?

Some classes may have several objects (or instances) in existence. An example of such a class is

St r i ng; a typical program contains many St r i ng objects at any moment in time.

Other classes may have only one or two instances. For example, high-level classes such as bank

and hotel reservation manager typically have only a single instance.

Note: There need not be any objects of a particular class at any particular point in time. For

example, if you have a banking system, you will not have any bank account objects until

someone opens a bank account.


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What Is Encapsulation?

Encapsulation hides the internal structure andoperations of an object behind an interface.

A bank ATM is an object that gives its users cash.

The ATM hides (encapsulates) the actual operation

of withdrawal from the user.

The interface (way to operate the ATM) is provided

by the keyboard functions, screen, cash dispenser,

and so on.

Bypassing the encapsulation is bank robbery.

Bypassing encapsulation in object-oriented

programming is impossible.

The Benefits of Encapsulation

With encapsulation, the developer can use an object and ignore the low-level details about how

the object is structured and how it works internally. This frees the developer to think at a higher

level of abstraction.

This results in the ability to comprehend more objects, and to understand more complex systems.

Comparing this with real life, if you had to understand how things worked before being able touse them, then you would not be able to deal with real-life objects such as ATMs, airplanes,microwave ovens, computers, or video recorders. To use these things, you deal with them by

using their interfaces and ignoring their implementations.An added benefit is that the implementation of the operations may change, and you should still

be able to use them in the usual manner.

Think again about the ATM. If the bank rewrites the software or changes the hardware of the

ATM, then it does not have to inform everyone how to use the new system. This is because the

interface has not changed; you still use the ATM in the same manner. When you see minor

changes to the interface of the ATM, it probably means that the software b

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