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Introduction to Java

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History of Java

• Java– Originally for intelligent consumer-electronic

devices

– Then used for creating Web pages with dynamic content

– Now also used to:• Develop large-scale enterprise applications

• Enhance WWW server functionality

• Provide applications for consumer devices (cell phones, etc.)

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Java Class Libraries

•Classes– Include methods that perform tasks• Return information after task completion

– Used to build Java programs

• Java provides class libraries– Known as Java APIs (Application Programming

Interfaces)

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FORTRAN, COBOL, Pascal and Ada

• FORTRAN– FORmula TRANslator

•COBOL– COmmon Business Oriented Language

• Pascal– Structured programming

•Ada– Multitasking

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BASIC, Visual Basic, Visual C++, C# and .NET

• BASIC– Beginner’s All-Purpose Symbolic Instruction Code

• .NET– .NET platform

•Visual Basic .NET– Based on BASIC

•Visual C++– Based on C++

•C#– Based on C++ and Java

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Typical Java Development Environment

• Java programs normally undergo five phases– Edit

• Programmer writes program (and stores program on disk)

– Compile• Compiler creates bytecodes from program

– Load• Class loader stores bytecodes in memory

– Verify• Bytecode Verifier confirms bytecodes do not violate security

restrictions

– Execute• JVM translates bytecodes into machine language

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Fig. 1.1 Typical Java development environment.

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Creating a Program with JCreator

•Click on the JCreator Icon

• IDE windowappears

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Creating a Program with JCreator

•Click on File, New, then Project

• Project Wizard appears– Choose Java Application template

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Creating a Program with JCreator

•Give the project a name

• Then click Next

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Creating a Program with JCreator

• You will want the JDK version 1.5

• This tab is where you can specify hsa library

At this point you can click on FinishAt this point you can click on Finish

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Creating a Program with JCreator

•Now we create our class (the program) with File, New, and Class

The Class Wizard appears. Specify a name for the class

and make sure Public is chosen

For now, you can proceed with Finish

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Creating a Program with JCreator

• The wizard creates a template.

•Now complete the program with the required commands.

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Creating a Program with JCreator

•Run the compiler with Build, and CompileFile

Build Output shows in bottom pane. This is where compiler error messages will be displayed.

Build Output shows in bottom pane. This is where compiler error messages will be displayed.

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Creating a Program with JCreator

• To run the compiled program click on Build, and ExecuteFile

• Program runs in separate window

Without Creating a ProjectWithout Creating a Project

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Programming with "Ready to Program"

• Find the "Ready" option on the program menu or click on the"Ready" icon

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Programming with "Ready to Program"

•An empty editor window appears

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Java Programs

•A Java program consists of one or more classes

The name of the file and the name of the class

must, that is MUST have the same name

The name of the file and the name of the class

must, that is MUST have the same name

Classes consist of a collection of

• Data items

• Methods

Classes consist of a collection of

• Data items

• Methods

A Java class with a method called

main() is a Java application.

A Java class with a method called

main() is a Java application.

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Creating a Java Application

• The "Ready" environment will give you skeleton or boilerplate format for programs

• Click on File, New, and HSA Console option

• A dialog box asksfor the name of the class

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Creating a Java Application

• The appropriate boilerplate text appears in the edit window – note the color coding

Bold Face Java keywords

Bold Face Java keywords Black

Identifiers in Java Class library

Black Identifiers in Java

Class library

BlueIdentifiers in

your program

BlueIdentifiers in

your program

GreenComments

GreenComments

RedQuoted Strings

RedQuoted Strings

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Creating a Java Application

• Fill in the necessary commands

• Save theprogram

Note that a dialog box will ask you for the nameBe sure to give it exactly the same name as the class

Note that a dialog box will ask you for the nameBe sure to give it exactly the same name as the class

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Creating a Java Application

• To run a Java program– Press the Run button or– Press Ctrl+R or– Press F1

• The consoleprogram showsa consolewindow

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Creating a Java Application

•Make sure to save the program before quitting

– The "Ready" environment will remind you

• To exit the "Ready" environment– Click the X close or

– Choose File, Exit or

– Use Ctrl-Q

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Creating a Java Application

• Errors in the program– Syntax errors are found for you by the compiler

Dialog box shows how many errors

Dialog box shows how many errors

Error line(s) highlighted

Error line(s) highlighted

Description of error given in the status bar

Description of error given in the status bar

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Why Different IDEs?

•Which one you use depends on what you are doing

– In class the Ready to Program IDE is easy to use, “quick and dirty”

– But … it does not support JDK 5.0

• JCreator– supports JDK 5.0

• Eclipse– a bit more complicated, but does a bit more– found to be a bit balky with some elements of JDK

5.0