Java Tutorial/Thread/Wait Notify

Monitor a thread"s status.

class MyThread extends Thread{
  boolean waiting= true;
  boolean ready= false;
  public void run() {
    String thrdName = Thread.currentThread().getName();
    System.out.println(thrdName + " starting.");
    while(waiting) 
      System.out.println("waiting:"+waiting); 
    System.out.println("waiting...");
    startWait(); 
    try {
      Thread.sleep(10000);
    } catch(Exception exc) {
      System.out.println(thrdName + " interrupted.");
    }
    System.out.println(thrdName + " terminating.");
  }
  synchronized void startWait() {
    try {
      while(!ready){ 
        wait();
      }
    } catch(InterruptedException exc) {
      System.out.println("wait() interrupted");
    }
  }
  synchronized void startWork() {
    ready = true;
    notify();
  }
}
public class Main {
  public static void main(String args[]) throws Exception{
      MyThread thrd = new MyThread();
      thrd.setName("MyThread #1");
      System.out.println(thrd.getName()+" Alive:"+thrd.isAlive()+" State:" + thrd.getState() );
      thrd.start();
      Thread.sleep(50);
      System.out.println(thrd.getName()+" Alive:"+thrd.isAlive()+" State:" + thrd.getState() );
      thrd.waiting = false;
      Thread.sleep(50); 
      System.out.println(thrd.getName()+" Alive:"+thrd.isAlive()+" State:" + thrd.getState() );
      thrd.startWork();
      Thread.sleep(50);
      System.out.println(thrd.getName()+" Alive:"+thrd.isAlive()+" State:" + thrd.getState() );
      if(thrd.isAlive()) 
        System.out.println("alive");
      System.out.println(thrd.getName()+" Alive:"+thrd.isAlive()+" State:" + thrd.getState() );
  }
}

Pausing a Thread: set boolean a variable that the thread checks occasionally

public class Main {
  public static void main(String[] argv) throws Exception {
    MyThread thread = new MyThread();
    thread.start();
    while (true) {
      synchronized (thread) {
        thread.pause = true;
      }
      synchronized (thread) {
        thread.pause = false;
        thread.notify();
      }
    }
  }
}
class MyThread extends Thread {
  boolean pause = false;
  public void run() {
    while (true) {
      synchronized (this) {
        while (pause) {
          try {
            wait();
          } catch (Exception e) {
          }
        }
      }
    }
  }
}

Stopping a Thread: set a boolean variable that the thread checks occasionally

public class Main {
  public static void main(String[] argv) throws Exception {
    MyThread thread = new MyThread();
    thread.start();
    thread.stop = true;
  }
}
class MyThread extends Thread {
  boolean stop = false;
  public void run() {
    while (true) {
      if (stop) {
        return;
      }
    }
  }
}

Use wait() and notify() from Object class

class MyResource {
  boolean ready = false;
  synchronized void waitFor() throws Exception {
    System.out.println(Thread.currentThread().getName()+ " is entering waitFor().");
      while (!ready)
        wait();
    System.out.println(Thread.currentThread().getName() + " resuming execution.");
  }
  synchronized void start() {
    ready = true;
    notify();
  }
}
class MyThread implements Runnable {
  MyResource myResource;
  MyThread(String name, MyResource so) {
    myResource = so;
    new Thread(this, name).start();
  }
  public void run() {
   
    try {
      myResource.waitFor();
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}
public class Main {
  public static void main(String args[]) throws Exception {
    MyResource sObj = new MyResource();
    new MyThread("MyThread", sObj);
    for (int i = 0; i < 10; i++) {
      Thread.sleep(50);
      System.out.print(".");
    }
    sObj.start();
  }
}