java Applet Introduction
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Applets are small Java programs that run in web browsers. They have a lifecycle with methods like init(), start(), paint(), stop(), and destroy() that get called at different points. The init() method initializes variables, start() runs when the applet is displayed, paint() redraws the output, stop() runs when the browser closes, and destroy() removes the applet from memory. Sample code shows an applet class that extends Applet and overrides these methods to track calls and draw status messages. The status window can also be used to display messages to users.
java Applet Introduction
- 1. Applet Class Applet Life cycle Applet Skeleton Applet Status Window
- 2. Applet Class • An applet is a small Internet-based program written in Java, a programming language for the Web, which can be downloaded by any computer • The applet is also able to run in HTML What Applets are? • Applets are dynamic (animations and graphics). • Applets are interactive programs (via GUI components). Features of an Applet • Provides facility for frames • Event handling facility and user Interaction • GUI user interface • Graphics and multimedia
- 4. Sample program of Applet import java.applet.*; import java.awt.*; import java.applet.Applet; public class Applet_Class extends Applet { public void paint(Graphics g) { g.drawString("hello world",20,20); } }
- 5. Applet Skeleton Init() • The init method is the first method to be called. • Used for Initialize variables. • Only once during the run time of applet Start() • It is called after the init() • Start method called each time of an applet’s displayed on screen. Paint() • Paint method is called each time your applet’s output must be redarwn. Stop() • Stop method is called when a browser close. • The running applet will get stop • The applet is in suspend state Destroy() • This method remove the applet completely from memory
- 6. import java.applet.*; import java.awt.*; import java.applet.Applet; public class Applet_Class extends Applet { private static int initcall, startcall, paintcall, stopcall, destroycall; public void init() { setBackground(Color.cyan); setForeground(Color.red); initcall=initcall+1; } public void start() { startcall=startcall+1; } public void stop() { stopcall=stopcall+1; g.drawString("stop method", 0,1); } public void destroy() { destroycall=destroycall+1; } public void paint(Graphics g) { paintcall=paintcall+1; g.drawString("init Method is called for : "+initcall,0,14); g.drawString("start Method is called for : "+startcall,0,30); g.drawString("paint Method is called for : "+paintcall,0,46); g.drawString("stop Method is called for : "+stopcall,0,62); g.drawString("destroy Method is called for : "+destroycall,0,78); showStatus("Demo of Applet Life Cycle"); } }
- 7. Using the Status Window import java.applet.*; import java.awt.*; import java.applet.Applet; public class Applet_Class extends Applet { public void init() { } public void paint(Graphics g) { g.drawString("hellow see status at bottom", 40,40); showStatus("yugandhar"); } }