Question

I have a problem with Threads in Java.
I would like to write a program where there is Class Main which has ArrayList of Threads of some class (Class Task) which just writes a letter and the number. Object Main just wakes one Thread from ArrayList and let it to do something while the same object(Main) sleeps another one.
But there is one problem even if I change the Main.ACTIVE to false it does not end all of the Threads some stay on, and it’s random, I just would like to make them end and write:

I am saying goodbay + character – sth like that

public class Main extends Thread {
    ArrayList<Thread> threads;
    static boolean ACTIVE = true;
    public Main() {
        super();
        threads = new ArrayList<Thread>();
    }

    public void run(){

        Object monitor = new Object();
        for (int i = 0; i <= 5; i++) {
            threads.add(new Thread(new Task(i + 65, monitor)));
        }

        long cT = System.currentTimeMillis();
        for (int i = 0; i < threads.size(); i++) {
            threads.get(i).start();
        }
        System.out.println("BEFORE synchronized(monitor)");
        synchronized(monitor){
            while (System.currentTimeMillis() - cT < 1000) {
                try{
                    monitor.notify();
                    Thread.sleep(50);
                    monitor.wait();
                } catch(Exception e){
                    e.printStackTrace();}
                }
                System.out.println("BEFORE ACTIVE= FALSE and after WHILE in Main");
                ACTIVE = false;
                for(int i  = 0; i < threads.size(); i++){
                    System.out.println(threads.get(i).getState());
                }
            }
            System.out.println("LAST COMMAND IN MAIN");
        }
    }

    public static void main(String[] args) {
        new Main().start();
        //new Thread(new Task(65)).start();
    }
}

And the Task Class

public class Task implements Runnable {
    int nr;
    char character;
    Object monitor;

    public Task(int literaASCII, Object monitor) {
        this.nr = 0;
        this.monitor = monitor;
        character = (char) (literaASCII);
    }

    @Override
    public void run() {
        synchronized (monitor) {
            while (Main.ACTIVE) {
                try {
                     System.out.println("ENTERING WHILE IN TASK");
                    monitor.wait();
                    System.out.print(nr + "" + character + ", ");
                    nr++;
                    int r = (int) ((Math.random() * 50) + 50); // <500ms,1000ms)
                    Thread.sleep(r);
                } catch (Exception e) {e.printStackTrace();}
                monitor.notify();
                 System.out.println("YYYYYYYYY");
            }
             System.out.println("AFTER WHILE IN Task");
        }
        System.out.println("I am saying goodbye " + character);
    }
}

Answer 1

Now naswer is

0A, 0B, 0C, 0D, 0E, 0F, 1A, 1B, 1C, 1D, 1E, 1F, WAITING
WAITING
WAITING
WAITING
WAITING
WAITING
LAST COMMAND IN MAIN

I added sleep after starting threads

import java.util.ArrayList;

public class Main extends Thread {
ArrayList<Thread> threads;
volatile static boolean ACTIVE = true;
public Main() {
    super();
    threads = new ArrayList<Thread>();
}

 public void run(){

Object monitor = new Object();
for (int i = 0; i <= 5; i++) {
  threads.add(new Thread(new Task(i + 65, monitor)));
}

long cT = System.currentTimeMillis();
for (int i = 0; i < threads.size(); i++) {
  threads.get(i).start();
}
try{Thread.sleep(50);}catch(Exception e){e.printStackTrace();}
 //   System.out.println("BEFORE synchronized(monitor)");
synchronized(monitor){
  while (System.currentTimeMillis() - cT < 1000) {
      try{

    monitor.notify();
    Thread.sleep(500);

    monitor.wait();}catch(Exception e){e.printStackTrace();}
  }
   //    System.out.println("BEFORE ACTIVE= FALSE and after WHILE in Main");
  ACTIVE = false;
  for(int i  = 0; i < threads.size(); i++){
      System.out.println(threads.get(i).getState());
  }


}
System.out.println("LAST COMMAND IN MAIN");

  }


  public static void main(String[] args) {
     new Main().start();
    //new Thread(new Task(65)).start();

}

}

and the TASK

public class Task implements Runnable {
int nr;
char character;
Object monitor;

public Task(int literaASCII, Object monitor) {
    this.nr = 0;
    this.monitor = monitor;
    character = (char) (literaASCII);
}

@Override
public void run() {
    synchronized (monitor) {
        while (Main.ACTIVE) {
            try {
//               System.out.println("ENTERING WHILE IN TASK");
                monitor.wait();
                System.out.print(nr + "" + character + ", ");
                nr++;
                int r = (int) ((Math.random() * 50) + 50); // <500ms,1000ms)

                Thread.sleep(r);
            } catch (Exception e) {e.printStackTrace();}
            monitor.notify();
    //       System.out.println("YYYYYYYYY");
        }
         System.out.println("AFTER WHILE IN Task");
    }
    System.out.println("I am saying goodbye " + character);
}

}