Introduction to Applet


What is an Applet?

According to Sun:-

“An applet is a small program that is intended not to be run on its own, but rather to be embedded inside another application.

  • An applet is a Java program that runs on a web page.
  • An applet is compiled on one computer and can run on another computer through a Java-enabled Web browser.
  • Applet viewer is a program that can run an applet.

Web Browsers Accessing a Web Page:

 Web Browsers Accessing a Web Page

Web Server Sending Response To Web Browser:

Web Server Sending Response To Web Browser

Web Server Sending Response To Web Browser:

Web Server Sending Response To Web Browser (2)

Advantages of an Applet:

  • It is simple to make it work across platform.
  • It runs in a sandbox, so the user does not need to trust the code, so it can work without security approval.
  • It is supported by most web browsers.
  • It will cache in most web browsers, so will quick to load when returning to a web page.
  • The applet can work on all installed versions of Java rather than just the latest plugin version only.
  • It can improve with use: after a first applet is run, the JVM is already running and starts quickly, benefiting regular users of Java.

Disadvantages of an Applet:

  • It requires the default plug-in, which isn’t available by default on all web browsers.
  • It can’t start up until the JVM is running, and this may have significant startup time the first time it is used.
  • It is considered to difficult to build and design a good user interface with than with HTML-based technologies.
Life Cycle of an Applet:
  • init – To initialize the applet each time it’s loaded (or reloaded).
  • start -To start the applet’s execution, such as when the applet’s loaded or when the user revisits a page that contains the applet.
  • stop -To stop the applet’s execution, such as when the user leaves the applet’s page or quits the browser.
  • destroy -To perform a final cleanup in preparation for unloading.

Not every applet needs to override every one of these methods.


Security Issues in Context of Applet:

  • Every browser implements security policies to keep applets from compromising system security.
  • Current browsers impose the following restrictions on any applet that is loaded over the network:
  • An applet cannot load libraries or define native methods.
  • It cannot ordinarily read or write files on the host that’s executing it.
  • It cannot make network connections except to the host that it came from.
  • It cannot start any program on the host that’s executing it.
  • It cannot read certain system properties.
  • Windows that an applet brings up look different than windows that an application brings up.



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