How to start anonymous thread class

I have the following code snippet:

public class A {
    public static void main(String[] arg) {
        new Thread() {
            public void run() {
                System.out.println("blah");
            }
        };
    }
}

Here, how do I call the start() method for the thread without creating an instance of the thread class?

You're already creating an instance of the Thread class - you're just not doing anything with it. You could call start() without even using a local variable:

new Thread()
{
    public void run() {
        System.out.println("blah");
    }
}.start();

... but personally I'd normally assign it to a local variable, do anything else you want (e.g. setting the name etc) and then start it:

Thread t = new Thread() {
    public void run() {
        System.out.println("blah");
    }
};
t.start();

Since anonymous classes extend the given class you can store them in a variable.

eg.

Thread t = new Thread()
{
    public void run() {
        System.out.println("blah");
    }
};
t.start();

Alternatively, you can just call the start method on the object you have immediately created.

new Thread()
{
    public void run() {
        System.out.println("blah");
    }
}.start();
// similar to new Thread().start();

Though personally, I would always advise creating an anonymous instance of Runnable rather than Thread as the compiler will warn you if you accidentally get the method signature wrong (for an anonymous class it will warn you anyway I think, as anonymous classes can't define new non-private methods).

eg

new Thread(new Runnable()
{
    @Override
    public void run() {
        System.out.println("blah");
    }
}).start();

Not exactly sure this is what you are asking but you can do something like:

new Thread() {
    public void run() {
        System.out.println("blah");
    }
}.start();

Notice the start() method at the end of the anonymous class. You create the thread object but you need to start it to actually get another running thread.

Better than creating an anonymous Thread class is to create an anonymous Runnable class:

new Thread(new Runnable() {
    public void run() {
        System.out.println("blah");
    }
}).start();

Instead overriding the run() method in the Thread you inject a target Runnable to be run by the new thread. This is a better pattern.