import java.util.concurrent.locks.Lock;

import java.util.concurrent.locks.ReentrantLock;

public class MainClass {

private static int flag = 0;

public static void main(String[] args) throws Exception {

final Lock lock = new ReentrantLock();

Thread a = new Thread(new Runnable() {//

@Override

public void run() {

while (flag <= 30) {

lock.lock();

if (flag % 3 == 0) {

System.out.println("A");

flag ++;

}

lock.unlock();

}

}

});

Thread b = new Thread(new Runnable() {

@Override

public void run() {

while (flag <= 30) {

lock.lock();

if (flag % 3 == 1) {

System.out.println("B");

flag ++;

}

lock.unlock();

}

}

});

Thread c = new Thread(new Runnable() {

@Override

public void run() {

while (flag <= 30) {

lock.lock();

if (flag % 3 == 2) {

System.out.println("C");

flag ++;

}

lock.unlock();

}

}

});

a.start();

b.start();

c.start();

}

}