Concept behind putting wait(),notify() methods in Object class [duplicate]

Answer 1

Wait and notify method always called on object so whether it may be Thread object or simple object (which does not extends Thread class) Given Example will clear your all the doubts.

I have called wait and notify on class ObjB and that is the Thread class so we can say that wait and notify are called on any object.

public class ThreadA {
    public static void main(String[] args){
        ObjB b = new ObjB();
        Threadc c = new Threadc(b); 
        ThreadD d = new ThreadD(b);
        d.setPriority(5);
        c.setPriority(1);
        d.start();
        c.start();
    }
}

class ObjB {
    int total;
    int count(){
        for(int i=0; i<100 ; i++){
            total += i;
        }
        return total;
    }}


class Threadc extends Thread{
    ObjB b;
    Threadc(ObjB objB){
        b= objB;
    }
    int total;
    @Override
    public void run(){
        System.out.print("Thread C run method");
        synchronized(b){
            total = b.count();
            System.out.print("Thread C notified called ");
            b.notify();
        }
    }
}

class ThreadD extends Thread{
    ObjB b;
    ThreadD(ObjB objB){
        b= objB;
    }
    int total;
    @Override
    public void run(){
        System.out.print("Thread D run method");
        synchronized(b){
            System.out.println("Waiting for b to complete...");
            try {
                b.wait();
                System.out.print("Thread C B value is" + b.total);
                } 
                catch (InterruptedException e) {
                    e.printStackTrace();
                }
        }
    }
}