Applets are Java programs that can be embedded in HTML pages and run in web browsers. An applet's lifecycle involves several method calls: init() is called once to initialize variables; start() restarts the applet after being stopped or loads it initially; paint() redraws the applet's output; stop() suspends threads when the applet is no longer visible; and destroy() removes the applet from memory, freeing resources. Applets allow making websites more dynamic but require the Java plugin and have security restrictions compared to standalone applications.

1. GUI IN JAVA
 What is an Applet?
Introduction
Applet is java program that can be embedded into HTML pages. Java applets run on the java
enables web browsers such as Mozilla and internet explorer. Applet is designed to run
remotely on the client browser, so there are some restrictions on it. Applet can't access
system resources on the local computer. Applets are used to make the web site more
dynamic and entertaining.
Advantages of Applet:
Applets are cross platform and can run on Windows, Mac OS and Linux platform
Applets can work all the version of Java Plug-in
Applets are supported by most web browsers
Applets are cached in most web browsers, so will be quick to load when returning to
a web page
User can also have full access to the machine if user allows
Disadvantages of Java Applet:
Java plug-in is required to run applet
Java applet requires JVM so first time it takes significant start-up time
If applet is not already cached in the machine, it will be downloaded from internet
and will take time
It’s difficult to design and build good user interface in applets compared to HTML
technology
Applet versus Application
Applets as previously described, are the small programs while applications are larger
programs.
Applets don't have the main method while in an application execution starts with
the main method.
Applets can run in our browser's window or in an appletviewer. To run the applet in
an appletviewer will be an advantage for debugging.
Applets are designed for the client site programming purpose while the applications
don't have such type of criteria.
Applet is the powerful tools because it covers half of the java language picture. Java
applets are the best way of creating the programs in java. There are a less number of
java programmers that have the hands on experience on java applications.
Applications are also the platform independent as well as byte oriented just like the
applets.

2. Applets are designed just for handling the client site problems. While the java
applications are designed to work with the client as well as server.
Applications are designed to exist in a secure area. While the applets are typically
used.
Applications and applets have much of the similarity such as both have most of the same
features and share the same resources. Applets are created by extending the
java.applet.Applet class while the java applications start execution from the main method.
Applications are not too small to embed into a html page so that the user can view the
application in your browser. On the other hand applet has the accessibility criteria of the
resources. The key feature is that while they have so many differences but both can perform
the same purpose.
 The Life cycle of an Applet
Introduction
In this Section you will learn about the lifecycle of an applet and different methods of an
applet. Applet runs in the browser and its lifecycle method are called by JVM when it is
loaded and destroyed. Here are the lifecycle methods of an Applet:
init( )
The init( ) method is the first method to be called. This is where you should initialize
variables. This method is called only once during the run time of your applet.
start( )

3. The start( ) method is called after init( ). It is also called to restart an applet after it has been
stopped. Whereas init( ) is called once—the first time an applet is loaded—start( ) is called
each time an applet’s HTML document is displayed onscreen. So, if a user leaves a web page
and comes back, the applet resumes execution at start( ).
paint( )
The paint( ) method is called each time your applet’s output must be redrawn. This situation
can occur for several reasons. For example, the window in which the applet is running may
be overwritten by another window and then uncovered. Or the applet window may be
minimized and then restored. paint( ) is also called when the applet begins execution.
Whatever the cause, whenever the applet must redraw its output, paint( ) is called. The
paint( ) method has one parameter of type Graphics. This parameter will contain the
graphics context, which describes the graphics environment in which the applet is running.
This context is used whenever output to the applet is required.
stop( )
The stop( ) method is called when a web browser leaves the HTML document containing the
applet—when it goes to another page, for example. When stop( ) is called, the applet is
probably running. You should use stop( ) to suspend threads that don’t need to run when
the applet is not visible. You can restart them when start( ) is called if the user returns to the
page.
destroy( )
The destroy( ) method is called when the environment determines that your applet needs
to be removed completely from memory. At this point, you should free up any resources the
applet may be using. The stop( ) method is always called before destroy( ).