How to know how many threads have been created and running?

Question

This is my simple program in Java:

public class Counter extends Thread {      public static void main(String args[]) {             Thread t1 = new Thread();         Thread t2 = new Thread();         t1.start();         t2.start();     } } 

I am using Windows Operating System 32-bit. My question is, how can we know how many Threads are created in the program and how many Threads are running? Is there any such tool?

Answer 1

System.out.println("Number of active threads from the given thread: " + Thread.activeCount());

Answer 2

Thread.getAllStackTraces() will give you a map where each Thread is key. You can then examine the state of each Thread and check thread.isAlive().

Map<Thread, StackTraceElement[]> threads = Thread.getAllStackTraces();