The functionalities of two lines of code

Question

I'm learning about the threads in Java. I want to know whether the following two pieces of code are the same:

 class B extends Thread {
    public void run() {
        doSomething();
    }
    public void doSomething() {}
}
class A extends Thread { 
    public void run() {
        new B().start();
    }
}

The second piece of code is changing the class A:

class A extends Thread {
        public void run() {
            new B().doSomething();
        }
}

When I read the code of my team's project, I find this problem: A thread invoking another thread without loop.

Answer 1

These two cases are not the same, as your question already suggests.

Assuming that in each case we enter the code by calling new A().start() , then the first example starts a thread (A) which starts another thread (B) which calls doSomething() .

The second case starts a single thread (A) which calls B.doSomething() . In this case we don't start a thread of type B, because we never call .start() on an instance of B.

Answer 2

In the first snippet you are actually creating a new thread and the invocation of doSomething() is in a separate thread to what A's run() method is running in,

In the second snippet you are execution B's doSomething() in the context (thread) that A is running in.