Getting Started

1
Getting Started

• Cognitive Systems Modeling Lab.

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Contents

• JDK 1.2 Installation
• HelloWorldApp Application
• HelloWordl Applet

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JDK 1.2 Installation

• JDK
• Java Development Kit
• Notepad
• Microsoft - Visual J
• SYMANTEC - Visual Café
• Inprise - Borland JBuilder
• Oracle - JDeveloper
• Metrowerks - CodeWarrior Professional

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JDK 1.2 Installation
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JDK 1.2 Installation
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JDK 1.2 Installation
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JDK 1.2 Installation
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JDK 1.2 Installation
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JDK 1.2 Installation
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JRE 1.2 Installation
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JDK 1.2 Installation
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JDK 1.2 Installation
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Hello World Application

• Create a Java Source File
• Compile the Source File
• Run the Application

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Create a Java Source File

• class HelloWorldApp
• public static void main(String args)
• System.out.println("Hello World!")
  //Display the string.

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The Anatomy of a Java Application

• Defining a Class
• The main Method
• Using Classes and Objects

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Defining a Class

• class HelloWorldApp . . . .
• Class Cefinition
• class name . . .

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The main Method

• public static void main(String args)
• . . . .
• Every Java application must contain a main method
  
• public indicates that the main method can be
  called by any object
• static indicates that the main method is a class
  method
• void indicates that the main method doesn't
  return any value

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Using Classes and Objects

• System.out.println("Hello World!")
• System.out is the full name of the out variable
  in the System class
• an instance of the PrintStream class
• a class provided with the Java development
  environment
• When the System class is loaded into the
  application, it instantiates PrintStream and
  assigns the new PrintStream object to the out
  class variable
• Now we have an instance of a class, we can call
  one of its instance methods

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Create a Java Source File

• Using a text editor, create a file named
  HelloWorldApp.java

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Compile the Source File

• UNIX javac HelloWorldApp.java
• Win32 javac HelloWorldApp.java

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Run the Application

• UNIX java HelloWorldApp
• Win32 java HelloWorldApp

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Hello World Applet

• Create a Java Source File
• Compile the Source File
• Create an HTML File that Includes the Applet
• Run the Applet

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Create a Java Source File

• import java.applet.Applet
• import java.awt.Graphics
• public class HelloWorld extends Applet
• public void paint(Graphics g)
• g.drawString("Hello world!", 50, 25)

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The Anatomy of a Java Applet

• Importing Classes and Packages
• Defining an Applet Subclass
• Implementing Applet Methods
• Running an Applet

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Importing Classes and Packages

• The first two lines of the following listing
  import two classes used in the applet
• import java.applet.Applet
• Import java.awt.Graphics
• The java.applet package
• classes that are essential to Java applets
• The java.awt package
• the most frequently used classes in the Abstract
  Window Toolkit (AWT), which provides the Java
  graphical user interface (GUI)

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Importing Classes and Packages

• public class HelloWorld extends
  java.applet.Applet public void
  paint(java.awt.Graphics g) g.drawString("Hello
  world!", 50, 25)

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Defining an Applet Subclass

• public class HelloWorld extends Applet .
• extends indicates that HelloWorld is a subclass
  of the Applet class
• Applet class
• browser loads a page containing an applet, the
  browser sends a request to the applet, telling
  the applet to initialize itself and start
  executing

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Implementing Applet Methods

• implement the paint method
• public void paint(Graphics g)
  g.drawString("Hello world!", 50, 25)
• applets can implement two more methods

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Running an Applet

• ltAPPLETgt tag
• browser should load the class whose compiled code
  HelloWorld.class
• browser looks for this file in the same directory
  as the HTML document that contains the tag
• browser creates an instance of the class
• If you include an applet twice in one page, the
  browser loads the class file once and creates two
  instances of the class.
• The WIDTH and HEIGHT attributes are like the same
  attributes in an ltIMGgt tag

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Create a Java Source File

• Create a file named HelloWorld.java

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Compile the Source File

• UNIX javac HelloWorld.java
• Win32 javac HelloWorld.java

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Create an HTML File that Includes the Applet

• ltHTMLgt
• ltHEADgt
• ltTITLEgt A Simple Program lt/TITLEgt
• lt/HEADgt
• ltBODYgt
• Here is the output of my program
• ltAPPLET CODE"HelloWorld.class" WIDTH150
  HEIGHT25gt
• lt/APPLETgt
• lt/BODYgt
• lt/HTMLgt

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Create an HTML File that Includes the Applet
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Run the Applet