Java Thread isAlive() Method Example

Java Thread Examples

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• Java Create Thread Example
• Java Create Thread using Runnable Interface Example
• Java Create Thread with Lambda Expression
• JJava Create Multiple Threads Example
• Java Thread sleep() Method Example
• Java Thread join() Method Example
• Java Thread interrupt() Method Example
• Java Thread isAlive() Method Example
• Java Thread setName() Method Example
• Java Thread setPriority() Method Example

This post describes the usage of the Java Thread isAlive() method with an example.

Java Thread isAlive() Method Overview

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.

Java Thread 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

Reference

https://www.javaguides.net/2018/09/thread-class-in-java.html