Java多线程编程中，为什么等待唤醒机制的锁对象要与业务对象分离？

public class Desk {

    private static Integer food = 0;
    private static final Object lock = new Object();

}

public class Cook extends Thread {

    @Override
    public void run() {
        synchronized (lock) {
            while (true) {
                if (food == 1) {
                    try {
                        lock.wait();
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    }
                } else {
                    food = 1;
                    System.out.println("厨师做菜" + food);
                    lock.notifyAll();
                }
            }
        }
    }

}

public class Foodie extends Thread {

    @Override
    public void run() {
        synchronized (lock) {
            while (true) {
                if (food == 0) {
                    try {
                        lock.wait();
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    }
                } else {
                    food = 0;
                    System.out.println("我吃了" + food);
                    lock.notifyAll();
                }
            }
        }
    }

}