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Java Applets Life-Cycle Methods

This blog post will guide you about the basics of Java Applet. This tutorial will teach you how to create small applets. So, What is an Applet in Java ? An Applet is a small java program that runs in a Java enabled web browser. Java Applet is a small piece of java code that is embedded into HTML page, which gets executed when the HTML page loads into the browser. Applet runs on the Client machine, while Servlet runs on Server side. They are rarely used to make website dynamic. Its secure and platform independent. They require JVM and Java enabled web browser such as IE, Mozilla etc, to get execute on client machine. Applets are embedded into HTML documents and has various methods in java.applet.Applet, which governs its life-cycle. Let us look into few of those :

Applet Life-Cycle Methods

1. public void init()

It is the first method that is invoked or called for an applet. Any initialization needed for an applet is performed in this method. It is launched by the system automatically when Java executes an applet. It performs small tasks such as loading images and reading parameters etc . Applets can be initialized by the constructors but init method is preferred for doing all the applet initialization.

2. public void start()

After Java calls init method, this method is executed next. It gets automatically called after init method completes execution. It is special method, when a user goes to any other website and finally returns back to html page of applet, this method is called again. All the tasks that we need to perform after applet gets loaded and after user revisits applet is written here. Generally, animation performing code or new start to a different thread is written here.

3. public void paint( Graphics g )

This method is called usually after init and start method gets executed. This method is called whenever applet needs to be redrawn in the browser window. If user covers applet window by a different window and later comes back to same window by uncovering, the paint method is called. This method has one parameter of type Graphics which performs actions involved with drawing. It is also used for displaying text, graphics etc.

4. public void stop()

This method is called when the user leaves the page on which applet is running. This method performs tasks of stopping execution of animations and threads. This method is called just after the destroy method.

5. public void destroy()

This method is called when the browser completely ends the applet and it is being removed from memory. This method is called when browser shuts down normally. The destroy method has the code that perform tasks that are required to clean up resources such as graphics object, threads etc allocated to the applet.
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