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Applet and Graphics Inheritance Hierarchy of GUI Classes Constructors and Methods of the class Component Constructors and Methods of the class Component Constructors and Methods of the class Component Constructors and Methods of the class Container Applets

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Applets l.jpg
Applets

  • Applet: a Java program that is embedded within a Web page and executed by a Web browser

  • Create an applet by extending the class JApplet

  • class JApplet contained in package javax.swing




Applets10 l.jpg
Applets

  • No main method

  • Methods init, start, and paint guaranteed to be invoked in sequence

  • To develop an applet

    • Override any/all of the methods above


Applet methods l.jpg
Applet Methods

  • init Method

    • Initializes variables

    • Gets data from user

    • Places various GUI components

  • paint Method

    • Performs output


Skeleton of a java applet l.jpg
Skeleton of a Java Applet

import java.awt.Graphics;

import javax.swing.JApplet;

public classWelcomeApplet extends JApplet

{

}


Applet displaying welcome message l.jpg
Applet Displaying Welcome Message

//Welcome Applet

import java.awt.Graphics;

import javax.swing.JApplet;

public class WelcomeApplet extends JApplet

{

public void paint(Graphics g)

{

super.paint(g); //Line 1

g.drawString(“Welcome to Java Programming”,

30, 30); //Lineƒ2

}

}



Class font l.jpg
class Font

  • Shows text in different fonts

  • Contained in package java.awt

  • Available fonts

    • Serif/SanSerif

    • Monospaced

    • Dialog/DialogInput

  • Arguments for constructor

    • String specifying the Font face name

    • int value specifying Font style

    • int value specifying Font size

      • Expressed in points (72 points = 1 inch)



Class color l.jpg
class Color

  • Shows text in different colors

  • Changes background color of component

  • Contained in package java.awt






Class graphics l.jpg
class Graphics

  • Provides methods for drawing items such as lines, ovals, and rectangles on the screen

  • Contains methods to set the properties of graphic elements including clipping area, fonts, and colors

  • Contained in the package java.awt






Differences between applets and gui applications l.jpg

Applets

Derived from JApplet

No main method

Uses init method

Displayed by HTML

Sets title in HTML

Size set in HTML

Applet closes when HTML doc closes

GUI applications

class extends JFrame

Invokes main method

Uses constructors

Uses method setVisible

Uses setTitle method

Uses method setSize

Closes with Exit button

Differences Between Applets and GUI Applications


Converting a gui application to an applet l.jpg
Converting a GUI Application to an Applet

  • Change JFrame to JApplet

  • Change constructor to method init

  • Remove method calls such as setVisible, setTitle, setSize

  • Remove the method main

  • If applicable, remove Exit button/all code associated with it (e.g. action listener)


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