ThreadGroup: activeCount() : ThreadGroup « java.lang « Java by API

1. Java by API
2. java.lang
3. ThreadGroup

ThreadGroup: activeCount()

 
/*
 * Output:
New thread: Thread[One,5,Group A]
New thread: Thread[Two,5,Group A]
One: 5
New thread: Thread[Three,5,Group B]
New thread: Thread[Four,5,Group B]

Here is output from list():
java.lang.ThreadGroup[name=Group A,maxpri=10]
    Thread[One,5,Group A]
    Thread[Two,5,Group A]
java.lang.ThreadGroup[name=Group B,maxpri=10]
    Thread[Three,5,Group B]
    Thread[Four,5,Group B]
Suspending Group A
Three: 5
Two: 5
Four: 5
Resuming Group A
Four: 4
Three: 4
Waiting for threads to finish.
Two: 4
 */

class MyThread extends Thread {
  boolean suspended;

  MyThread(String threadname, ThreadGroup tgOb) {
    super(tgOb, threadname);
    System.out.println("New thread: " + this);
    suspended = false;
    start(); // Start the thread
  }

  public void run() {
    try {
      for (int i = 5; i > 0; i--) {
        System.out.println(getName() + ": " + i);
        Thread.sleep(1000);
        synchronized (this) {
          while (suspended) {
            wait();
          }
        }
      }
    } catch (Exception e) {
      System.out.println("Exception in " + getName());
    }
    System.out.println(getName() + " exiting.");
  }

  void suspendMe() {
    suspended = true;
  }

  synchronized void resumeMe() {
    suspended = false;
    notify();
  }
}

public class MainClass {
  public static void main(String args[]) {
    ThreadGroup groupA = new ThreadGroup("Group A");
    ThreadGroup groupB = new ThreadGroup("Group B");

    MyThread ob1 = new MyThread("One", groupA);
    MyThread ob2 = new MyThread("Two", groupA);
    MyThread ob3 = new MyThread("Three", groupB);
    MyThread ob4 = new MyThread("Four", groupB);

    System.out.println("\nHere is output from list():");
    groupA.list();
    groupB.list();

    System.out.println("Suspending Group A");
    Thread tga[] = new Thread[groupA.activeCount()];
    groupA.enumerate(tga); // get threads in group
    for (int i = 0; i < tga.length; i++) {
      ((MyThread) tga[i]).suspendMe(); // suspend each thread
    }

    try {
      Thread.sleep(1000);
    } catch (InterruptedException e) {
      System.out.println("Main thread interrupted.");
    }

    System.out.println("Resuming Group A");
    for (int i = 0; i < tga.length; i++) {
      ((MyThread) tga[i]).resumeMe();
    }

    try {
      System.out.println("Waiting for threads to finish.");
      ob1.join();
      ob2.join();
      ob3.join();
      ob4.join();
    } catch (Exception e) {
      System.out.println("Exception in Main thread");
    }
    System.out.println("Main thread exiting.");
  }
}


           
         
  

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