public class Monitor {
    int count = 0;
    public synchronized void aa(int n){
        while (n > 0){
            try {
                count++;
                wait();
                n--;
            }catch (InterruptedException e){}
        }
        System.out.println("count before="+count);
        notifyAll();
        System.out.println("count after="+count);
    }

    public static void main(String[]args){
        Monitor m = new Monitor();
        Thread t1 = new T(2, m);
        Thread t2 = new T(1, m);
        Thread t3 = new T(0, m);
        try{
            t1.start();
            t2.start();
            t3.start();
        } catch (Exception e){}
    }
}


class T extends Thread {
    private Monitor m;
    public int par;

    public T(int par, Monitor m){
        this.m = m;
        this.par = par;
    }

    @Override
    public void run() {
        m.aa(par);
    }
}

t1 -> count++ (count is now 1), wait()
t2 -> count++ (count is now 2), wait()
t3 -> notifyAll() -> t2 wakes up.
t2 -> notifyAll() -> t1 wakes up
t1 -> count++ (count is now 3), wait().

count before=2
count after=2
count before=2
count after=2

public class Monitor {
    int count = 0;
    public synchronized void aa(int n){
        while (n > 0){
            try {
                count++;
                wait();
                n--;
            }catch (InterruptedException e){}
        }
        System.out.println("count before="+count);
        notify();
        System.out.println("count after="+count);
    }

    public static void main(String[]args){
        Monitor m = new Monitor();
        Thread t1 = new T(2, m);
        Thread t2 = new T(1, m);
        Thread t3 = new T(0, m);
        try{
            t1.start();
            t2.start();
            t3.start();
        } catch (Exception e){}
    }
}


class T extends Thread {
    private Monitor m;
    public int par;

    public T(int par, Monitor m){
        this.m = m;
        this.par = par;
    }

    @Override
    public void run() {
        m.aa(par);
    }
}

t1 -> count++ (count is now 1), wait()
t2 -> count++ (count is now 2), wait()
t3 -> notify() -> t1 wakes up.
t1 -> count++ (count is now 3) wait().

count before=2
count after=2