The main
method is the entry point of a Java application.
Specifically?when the Java Virtual Machine is told to run an application by specifying its class (by using the java
application launcher), it will look for the main
method with the signature of public static void main(String[])
.
From Sun's java
command page:
The java tool launches a Java application. It does this by starting a Java runtime environment, loading a specified class, and invoking that class's main method.
The method must be declared public and static, it must not return any value, and it must accept a
String
array as a parameter. The method declaration must look like the following:public static void main(String args[])
For additional resources on how an Java application is executed, please refer to the following sources:
The run
method is the entry point for a new Thread
or an class implementing the Runnable
interface. It is not called by the Java Virutal Machine when it is started up by the java
command.
As a Thread
or Runnable
itself cannot be run directly by the Java Virtual Machine, so it must be invoked by the Thread.start()
method. This can be accomplished by instantiating a Thread
and calling its start
method in the main
method of the application:
public class MyRunnable implements Runnable
{
public void run()
{
System.out.println("Hello World!");
}
public static void main(String[] args)
{
new Thread(new MyRunnable()).start();
}
}
For more information and an example of how to start a subclass of Thread
or a class implementing Runnable
, see Defining and Starting a Thread from the Java Tutorials.
The init
method is the first method called in an Applet or JApplet.
When an applet is loaded by the Java plugin of a browser or by an applet viewer, it will first call the Applet.init
method. Any initializations that are required to use the applet should be executed here. After the init
method is complete, the start
method is called.
For more information about when the init
method of an applet is called, please read about the lifecycle of an applet at The Life Cycle of an Applet from the Java Tutorials.
See also: How to Make Applets from the Java Tutorial.