Thread: Java Main Method

Originally Posted by Graham

It is actually possible to run an app without a main method, for example:

Code:

public final class NoMainMethod {
	
	static {
		System.out.println("I have no main method, but can still do stuff!");
		System.exit(0); // required to stop NoSuchMethodError
	}
	
}

Run like so:

Code:

[email protected]:~/test$ java NoMainMethod 
I have no main method, but can still do stuff!
[email protected]:~/test$

This works because when the class is loaded, the contents of the static initializer are executed by the class loader. Then it quits the application to prevent the NoSuchMethodError from being shown. However, I wouldn't recommend doing this!

If you are developing an applet, your app won't have a main method. Instead, you subclass applet and specify the the applet to load in the <applet> tag. However, ultimately, somewhere along the line there is a main() method (or that nasty trick, unlikely to see that in production code though) which then goes and calls the appropriate applet method.

There are probably other situations where you won't have a main() method, e.g. if you are writing an app to instrument another app you'll have a premain() method instead. If you are writing a J2EE app, you'll just have a collection of servlets (and some convoluted xml files defining them). Kind of like the applets, another program (the application server) starts it for you.

Thanks for sharing your knowledge, Graham. But from what you have just told me i get a strong impression its best to have a main method in Java SE programs, despite being able to do otherwise.

Originally Posted by PSNB

Exactly. Only when developing applications though. When developing applets, you use the four methods that are overridden by the applet, which are

1. init()
2. start()
3. stop()
4. destroy()

Thanks PSNB. Whats the difference between an applet and an application? Is an RSPS an applet of application?