Java Thread is isAlive Method Example

In this article, we will learn java.lang.Thread class provides isAlive() method to test if this thread is alive or not. A thread is alive if it has been started and has not yet died.

In this article, we will discuss the usage of isAlive() method with an example.

Thread is isAlive Method Example

1. Let's create two threads

final Thread thread1 = new Thread(new MyTask());
final Thread thread2 = new Thread(new MyTask());

2. Before starting the threads with start() method, just print to check whether the threads are alive or not.

System.out.println("Thread1 is alive? " + thread1.isAlive());
System.out.println("Thread2 is alive? " + thread2.isAlive());

3. Start the threads and check again to check whether the threads are alive or not

thread1.start();
thread2.start();

while (thread1.isAlive() || thread2.isAlive()) {
	System.out.println("Thread1 is alive? " + thread1.isAlive());
	System.out.println("Thread2 is alive? " + thread2.isAlive());
	Thread.sleep(500l);
}

Let's put all together and the complete program:

public class CheckIfThreadIsAliveUsingThreadAPI {

	public static void main(final String[] args) throws InterruptedException {

		System.out.println("Thread main started");

		final Thread thread1 = new Thread(new MyTask());
		final Thread thread2 = new Thread(new MyTask());

		System.out.println("Thread1 is alive? " + thread1.isAlive());
		System.out.println("Thread2 is alive? " + thread2.isAlive());

		thread1.start();
		thread2.start();

		while (thread1.isAlive() || thread2.isAlive()) {
			System.out.println("Thread1 is alive? " + thread1.isAlive());
			System.out.println("Thread2 is alive? " + thread2.isAlive());
			Thread.sleep(500l);
		}

		System.out.println("Thread1 is alive? " + thread1.isAlive());
		System.out.println("Thread2 is alive? " + thread2.isAlive());
		
		System.out.println("Thread main finished");
	}
}

class MyTask implements Runnable {
	@Override
	public void run() {
		for (int i = 0; i < 5; i++) {
			System.out.println("[" + Thread.currentThread().getName() + "] Message " + i);
			try {
				Thread.sleep(200);
			} catch (final InterruptedException e) {
				e.printStackTrace();
			}
		}
	}
}

Output:

Thread main started
Thread1 is alive? false
Thread2 is alive? false
Thread1 is alive? true
Thread2 is alive? true
[Thread-0] Message 0
[Thread-1] Message 0
[Thread-1] Message 1
[Thread-0] Message 1
[Thread-1] Message 2
[Thread-0] Message 2
Thread1 is alive? true
Thread2 is alive? true
[Thread-0] Message 3
[Thread-1] Message 3
[Thread-1] Message 4
[Thread-0] Message 4
Thread1 is alive? false
Thread2 is alive? false
Thread main finished