Threads

import java.util.concurrent.locks.ReentrantLock;

class Program {

    public static void main(String[] args) throws InterruptedException{
        Number n = new Number(0);
        int cnt = 100;
        Thread[] th = new Thread[cnt];

        for (int i = 0; i < cnt; i++){
            th[i] = new Thread(new Increment(n));
        }
        for (int i = 0; i < cnt; i++){
            th[i].start();
        }
        for (int i = 0; i < cnt; i++){
            th[i].join();
        }
        System.out.println("Number = " + (n.value));
    }

}

class Increment implements Runnable {
    Number num;
    public Increment (Number n){
        this.num = n;
    }
    @Override
    public void run() {
        for (int i = 0; i < 100; i++){
             num.increment(); // i++
        }
    }
}

class Number {
    ReentrantLock lock = new ReentrantLock();
    public int value;
    public Number(int value){
        this.value = value;
    }
    public synchronized void increment(){
       // lock.lock();
        this.value++;
       // lock.unlock();
    }
}