Clientside Dynamic Programming: Applet

1
Client-side Dynamic Programming Applet

• Dan Wang

2
Introduction

• What is Applet?
• Applet is a software component that runs in the
  browser
• Applet is not a program
• It cannot run independently.
• It must run in a container (browser).
• Applet is not a subroutine or a function.
• It can implement a complete web component.
• Applets can enhance the capability of interacting
  between the user and their host program.

3
Introduction

• How to create an Applet?
• Ex1 A simple applet Hello, World!
• Generate the bytecode FirstApplet.class
• javac FirstApplet.java
• Use HTML document to embed the Applet

import java.applet. import java.awt. public
class FirstApplet extends Applet public void
paint(Graphics g) g.drawString("Hello,
World!", 25, 50)
4
Embedded in HTML Document

• HTML uses ltappletgt tags to embed an applet
• ltapplet codeapplet-name.class width
  height codebaseapplet-URL namegt
• ltparam namepar1 valueval1gt
• ltparam namepar2 valueval2gt
• lt/appletgt

5
Lifetime of an Applet

• The lifetime of an applet depends on the web
  page.
• When a web page is loaded, the applet is
  initialized and started.
• When the user leaves the web page, the applet
  stops.
• When the browser is closed, the applet is
  finalized.

Start()
Stop()
Final()
Init()
6
Execution of Applet

• When the web page with an applet is loaded, the
  browser will do the following
• Search the bytecode of the applet class defined
  in the ltappletgt tag. The URL location is
  determined by the codebase attribute
• Load the bytecode to the user machine
• Create an instance of the applet class
• Call init() to initialize the applet instance
• Call start() to execute the instance
• When leave the page, call stop() to stop the
  execution
• When return to the page again, call start() to
  restore the execution.
• When the browser is closed, the applet is
  finalized.

Start()
Stop()
Final()
Init()
7
More Examples

• Ex1 A simple applet Hello, World!
• Source file FirstApplet.java
• Ex2 Drawing something in an applet
• Source file SecondApplet.java
• Ex3 Processing event in an applet
• Source file EventTester.java
• Ex4 Get parameters from HTML file
• Source file ColorScribble.java
• Ex5 Add a button in an applet
• Source file ClearableScribble.java