this and static method

[Bin Wang]

public class ThreadTest extends Thread {
public void run() {
System.out.println("Before sleep");
try {
this.sleep(1000);
}
catch (InterruptedException ie) { }
System.out.println("After sleep");
}

public static void main(String[] args) {
ThreadTest a = new ThreadTest();
a.start();
}
}
The above program compile and run. Can somebody explain why this.sleep(1000) works here? Is it because sleep() is used in the run() method which is non-static?

[Vanitha Sugumaran]

Hi,
"this" in a method means the object that was invoked.
so we can't use "this" in a static method, which applies for the whole class not for an instance.
Vanitha.

[Ranjan Chaudhuri]

Yes, this.sleep() works because you're invoking it from a non-static method. But you don't really need the "this" because sleep(msec) is itself a static method of class Thread. So you could call it from a static method without using the "this" reference.

Ranjan

[Bin Wang]

thanks guys.
In fact, "this" can't be used in a static method. It'll cause compile error.