Using notifyAll()

package com.thread;

public class Reader extends Thread {
 Calculator c;
 
 public Reader(Calculator calc) {
  c = calc;
 }
 
 public void run() {
  synchronized(c) {
   try {
    System.out.println("Waiting for calculation...");
    c.wait();
   } catch (InterruptedException e) {
    
   }
   System.out.println("Total is: " + c.total);
  }
 }
 
 public static void main(String[] args) {
  Calculator calculator = new Calculator();
  
  // starts three threads that are all waiting to receive 
  // the finished calculation
  new Reader(calculator).start();
  new Reader(calculator).start();
  new Reader(calculator).start();
  
  // start the calculator with its calculation
  calculator.start();
 }
}

class Calculator extends Thread {
 int total;
 
 public void run() {
  synchronized(this) {
   for(int i = 0; i < 100; i ++) {
    total += i;
   }
   notifyAll();
  }
 }
}