Thread isAlive() Method

• isAlive() method checks whether a thread is currently running or not.
• If the thread has been started and not yet died, it will return true, otherwise it will return false.
• Use :-
  • Determine if a thread is still executing for control or debugging purposes.
  • Avoid performing operations on threads that have already completed.
  • Useful for thread management in multi-threaded applications or thread pools.
• Syntax :-
  • public final boolean isAlive()
• Program :-

  class MyTask extends Thread
  {
      @Override
      public void run()
      {
          System.out.println(getName() + " is running.");
          for (int i = 1; i <= 5; i++)
          {
              System.out.println(getName() + " count: " + i);
          }
          System.out.println(getName() + " finished execution.");
      }
  }
  
  public class IsAliveSimpleDemo
  {
      public static void main(String[] args) throws Exception
      {
          MyTask t1 = new MyTask();
          t1.setName("Thread-1");
  
          System.out.println("Before start: " + t1.isAlive()); // false
  
          t1.start();
          System.out.println("After start: " + t1.isAlive()); // true (likely)
  
          // pause thread for 1 second
          Thread.sleep(1000);
  
          System.out.println("After completion: " + t1.isAlive()); // false
      }
  }

  Output (sample):

  Before start: false
  After start: true
  Thread-1 is running.
  Thread-1 count: 1
  Thread-1 count: 2
  Thread-1 count: 3
  Thread-1 count: 4
  Thread-1 count: 5
  Thread-1 finished execution.
  After completion: false

• Other key points :-
  • isAlive() returns true only after start() is called and before the thread dies.
  • It is final method, cannot be overridden.
  • It is useful for monitoring thread state in concurrent programs.
  • It does not block the calling thread — it simply returns the status.