What is the importance of join() method in Java?

public final void join() throws InterruptedException

public class JoinTest extends Thread {
   public void run() {
      for(int i=1; i <= 3; i++) {
         try {
            Thread.sleep(1000);
         } catch(Exception e) {
            System.out.println(e);
         }
         System.out.println("TutorialsPoint "+ i);
      }
   }
   public static void main(String args[]) {
      JoinTest t1 = new JoinTest();
      JoinTest t2 = new JoinTest();
      JoinTest t3 = new JoinTest();
      t1.start();
      try {
<strong>         t1.join(); // calling join() method
</strong>      } catch(Exception e) {
         System.out.println(e);
      }
      t2.start();
      t3.start();
   }
}

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