need answers to this java program

[peixd]

hello,everyone. i am a new commer. i read the java tutorial. then i hava got a question. the source code is as follows:

public class SimpleThreads {

  // Display a message, preceded by the name
  // of the current thread
  static void threadMessage(String message) {
    String threadName = Thread.currentThread().getName();
    System.out.format("%s: %s%n", threadName, message);
  }

  private static class MessageLoop implements Runnable {
    public void run() {
      String importantInfo[] = {
        "Mares eat oats",
        "Does eat oats",
        "Little lambs eat ivy",
        "A kid will eat ivy too"
      };
      try {
        for (int i = 0; i < importantInfo.length; i++) {
          // Pause for 4 seconds
          Thread.sleep(4000);
          // Print a message
          threadMessage(importantInfo[i]);
        }
      } catch (InterruptedException e) {
          threadMessage("I wasn't done!");
      }
    }
  }

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

    // Delay, in milliseconds before we interrupt MessageLoop
    // thread (default one hour).
    long patience = 1000 * 60 * 60;

    // If command line argument present,
    // gives patience in seconds.
    if (args.length > 0) {
      try {
          patience = Long.parseLong(args[0]) * 1000;
      } catch (NumberFormatException e) {
          System.err.println("Argument must be an integer.");
          System.exit(1);
      }
    }

    threadMessage("Starting MessageLoop thread");
    long startTime = System.currentTimeMillis();
    Thread t = new Thread(new MessageLoop());
    t.start();

    threadMessage("Waiting for MessageLoop thread to finish");
    // loop until MessageLoop thread exits
    while (t.isAlive()) {
      threadMessage("Still waiting...");
      // Wait maximum of 1 second for MessageLoop thread to
      // finish.
      t.join(1000);
      if (((System.currentTimeMillis() - startTime) > patience)
                                              && t.isAlive()) {
        threadMessage("Tired of waiting!");
        t.interrupt();
        // Shouldn't be long now -- wait indefinitely
        t.join();
      }

    }
    threadMessage("Finally!");
  }
}

in the WHILE block, is the t.join() necessary ? the t.interrupt has made the t thread interrupted, why does the main thread still have to wait the t thread to finish?

[Eranga]

Please use code tags when you posting again in the forum. Unformated codes are really hard to read. If you don't know how to do it, please check on my forum signature.

[Eranga]

in the WHILE block, is the t.join() necessary ?

What really join() does? Did you read about that in API?