Given the following program class Game { private static final int DELAY = 500; private int x; public Game() { x = 0; } public void addX() { try { int y = x; Thread.sleep((int) (DELAY * Math.random())); y += 1; x = y; System.out.println("x=" + x); } catch (InterruptedException e) { } } } public class Homework8 { public static void main(String[] args) { var game = new Game(); for (int i = 0; i < 2; i++) { new Thread(() -> { for (int j = 0; j < 2; j++) game.addX(); }).start(); } } } The output could be x=1 x=1 x=2 x=2 or x=1 x=2 x=1 x=2 However, we desire the output to be x=1 x=2 x=3 x=4 1. Modify the addX method using ReentrantLock to get the desired output.

To get the desired output of x=1 x=2 x=3 x=4, we can also use the ReentrantLock mechanism to synchronize the threads. Here's the modified Game class with ReentrantLock:

import java.util.concurrent.locks.ReentrantLock;

class Game {
    private static final int DELAY = 500;
    private int x;
    private final ReentrantLock lock = new ReentrantLock();

    public Game() {
        x = 0;
    }

    public void addX() {
        lock.lock();
        try {
            int y = x;
            Thread.sleep((int) (DELAY * Math.random()));
            y += 1;
            x = y;
            System.out.println("x=" + x);
        } catch (InterruptedException e) {
        } finally {
            lock.unlock();
        }
    }
}

In the modified addX() method, we have created a ReentrantLock object and used the lock() and unlock() methods to ensure that only one thread can execute the method at a time. This will prevent two threads from accessing and modifying the x variable at the same time, which was causing the wrong output.

Now, when we run the Homework8 class with the modified Game class, the output will always be x=1 x=2 x=3 x=4.