How does the getName in Thead works ?

[Vinay Kumar T M]

Hi,

Just started learning Threads for my certification but my curiosity drove me beyond certificaton objectives.

I tried to find the Thread class source code but could not fully understand.

in my PSVM(test class - public static class void main) method, I am coding the below code (where class B extends Thead)
B b = new B("b");
Compiler forces me to use the below constructor
B(String s) {} //It does not force me to pass s to the super constructor

My question is

super() statement is added by default, when we inherit. I also know there is a no-arg constructo in Thread class, so compiler wont complain. So, all Ok, untill now.
but how does b.getName() returns "b" ?
Constructor of B don't even pass "b" to super class, so super class dont know anything about the name "b", so it returns "Thread-0" in my JVM implementation.  
However, If I add super(s) statement inside B's constructor, I get the name displayed as b.

I am new to java, but I am missing some fundamentals here. Please help me.

b.getName() for sure refers to the method in Thread class (as B extends Thread, and class B has not overridden getName() method). at somepoint later, If I execute the statment, b.getName(), I get "b". I actually expect "Thread-0". I am wondering, how did the name instance b is aware of his name "b".  (in otherwords how was the name passed  up in the hierarchy in constructors).

This is interesting topic to me, but I might not be clear. So, to be clear, I paste my playing code here, so you get a picture of me. I have lot of commented code, so please bear with me

public class ThreadDemo {

	public static void main(String[] args) {
		Thread t = new Thread("t");
//		{
//			public void run(){
//				System.out.println("inside anonymous new Thread");
//			}
//		};
//		t.start();

//		A a = new A();
//		a.run();
		

		B b = new B("b");
//		b.start();
		b.run();
		System.out.println(Thread.currentThread().getName());
		
		print(Thread.currentThread());
		print(t);
	print(b);
	
	for (StackTraceElement s : t.getStackTrace()) {
		System.out.println(s.getMethodName());
	}

	}

	static void print(Thread t){
		System.out.println(
				"Thread name : " +
		t.getName()
		+"  ,  "+
		t.getId()
				+"  ,  "+
				t.getPriority()
				+"  ,  "+
				t.isAlive()
				+"  ,  "+
				t.getState()
		);
	}
	
}

//class A implements Runnable {
//
//	public void run() {
//		System.out.println("Inside Run method of Class A");
//		
//	}
//
//}

class B extends Thread {
	 B(String s) {
//		super(s);
//		System.out.println(super.getName());
	}

	public void run() {
		System.out.println("Inside Run method of Class B");
//		try {
//			Thread.sleep(2000l);
//		} catch (InterruptedException e) {
//			e.printStackTrace();
//		}
	}

}

[Piet Souris]

hi Vinay,

if I run your code, then this is the output that I get (for technical reasons I had to name your classs B as B2):

Inside Run method of Class B2
main
Thread name : main  ,  1  ,  5  ,  true  ,  RUNNABLE
Thread name : t  ,  10  ,  5  ,  false  ,  NEW
Thread name : Thread-0  ,  11  ,  5  ,  false  ,  NEW

so I do get the expected result. Can you elaborate a little on your outcome of "b"?

[Vinay Kumar T M]

Hi,

My bad. I think I have overlooked it. Thanks for the help.

I see the correct output.