Applications and Applets An applet is a program delivered via the - - PowerPoint PPT Presentation

Duke CPS 108

• 19. 1

Applications and Applets

• An applet is a program delivered via the web

➤ security issues, sandbox model ➤ where does code/images/etc come from? How is it

delivered?

➤ what browsers support the 1.1 AWT event model (what

about 1.2)?

• Use IE 4, Netscape 4 (patched), appletviewer to run an applet,

appletviewer is good for debugging

• Possible to wrap up lots of classes in a .jar file

➤ java archive, similar to a tar file, possible to include .class

files, .au, .gif, etc, so all code transferred at once

Duke CPS 108

• 19. 2

Running an Applet

• An applet has an init() method

➤ similar to constructor, called only once, when the applet is

first loaded

• An applet has a start() method

➤ called each time the applet becomes “active”, run the first

time, or revisited e.g., via the back button in a browser

• An applet has a stop() method

➤ called when applet is invisible, e.g., user scrolls or goes to

another web page

• other methods in an applet

➤ destroy, getAppletInfo, getParameterInfo

• Applet subclasses Panel, so it is an Container/Component

Duke CPS 108

• 19. 3

Thread

• Threads are “lightweight” processes

➤ have access to same memory as other threads in the main

process

➤ each thread runs as a separate control, on a multiprocessor

these could be running simultaneously

➤ threads should each get a “time-slice” to run fairly

• Threads are created by subclassing Thread or implementing

Runnable

➤ Threads have a run method, this is where the action is, but

run is not called directly, only via Thread.start()

• Must be careful when many threads access the same object,

synchronization is needed