Explain init(), start(), stop(), and destroy() method?

The init() method is known as exactly once in an applet's life, while the applet is first loaded. It's generally used to read PARAM tags, start downloading any other images or media files you required, and set up the user interface. Most applets have init() methods.

The start() method is called at least once in an applet's life, while the applet is begin or restarted. In some cases it may be known as more than once. Several applets you write will not have explicit start()methods and will merely inherit one from their superclass. A start() method is frequent used to start any threads the applet will required while it runs.

The stop() method is known as at least once in an applet's life, while the browser leaves the page in that case the applet is embedded. The applet's start() method will be called if at some later point the browser returns to the page containing the applet. In some cases the stop() method may be called multiple times in an applet's life. Several applets you write will not have explicit stop()methods and will merely inherit one from their superclass. Your applet should use the stop() method to pause any running threads. When your applet is stopped, it should not use any CPU cycles.

The destroy() method is known as exactly once in an applet's life, just before the browser unloads the applet. This method is commonly used to perform any final clean-up. For example, an applet that stores state on the server might send some data back to the server before it's terminated. many applets will not have explicit destroy() methods and just inherit one from their superclass.

For example, in a video applet, the init() method might draw the controls and start loading the video file. The start() method would wait until the file was loaded, and then start playing it. The stop() method would pause the video, but not rewind it. If the start() method were called again, the video would pick up where it left off; it would not start over from the beginning. However, if destroy() were called and then init(), the video would start over from the beginning.

In the JDK's appletviewer, selecting the Restart menu item calls stop() and then start(). Selecting the Reload menu item calls stop(), destroy(), and init(), in that order. (Generally the byte codes will also be reloaded and the HTML file reread by Netscape has a problem with this.)

The applet start() and stop() methods are not related to the same named methods in the java.lang.Thread class.
Your own code may occasionally invoke start() and stop(). For example, it's customary to stop playing an animation when the user clicks the mouse in the applet and restart it when they click the mouse again.

Your own code can also invoke init() and destroy(), but this is normally a bad idea. Only the environment should call init() and destroy().