public class BreakfastQueue { private static int count = 0; private static int money = 0; private static Object lock = new Object(); public static void main(String[] args) { BreakfastShop shop = new BreakfastShop(); new Thread(new Customer("张先生", 20, shop)).start(); new Thread(new Customer("王先生", 10, shop)).start(); new Thread(new Customer("李先生", 5, shop)).start(); } static class BreakfastShop { public void sell() { synchronized (lock) { while (count >= 3) { try { lock.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } count++; money += 5; System.out.println(Thread.currentThread().getName() + " 买了早餐，共有 " + count + " 人排队，收入 " + money + " 元"); lock.notifyAll(); } } } static class Customer implements Runnable { private String name; private int money; private BreakfastShop shop; public Customer(String name, int money, BreakfastShop shop) { this.name = name; this.money = money; this.shop = shop; } @Override public void run() { while (true) { if (money >= 5) { shop.sell(); money -= 5; } else if (money == 0) { System.out.println(name + " 没钱了，回家了"); break; } else { System.out.println(name + " 余额不足，等待中..."); try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } } } } } }优化以上代码

以下是改进后的代码：

public class BreakfastQueue {
    private int count = 0;
    private int money = 0;
    private Object lock = new Object();

    public static void main(String[] args) {
        BreakfastShop shop = new BreakfastShop();
        new Thread(new Customer("张先生", 20, shop)).start();
        new Thread(new Customer("王先生", 10, shop)).start();
        new Thread(new Customer("李先生", 5, shop)).start();
    }

    class BreakfastShop {
        public void sell() {
            synchronized (lock) {
                if (count >= 3) {
                    try {
                        lock.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                count++;
                money += 5;
                System.out.println(Thread.currentThread().getName() + " 买了早餐，共有 " + count + " 人排队，收入 " + money + " 元");
                lock.notifyAll();
            }
        }
    }

    class Customer implements Runnable {
        private String name;
        private int money;
        private BreakfastShop shop;
        private boolean flag = false;

        public Customer(String name, int money, BreakfastShop shop) {
            this.name = name;
            this.money = money;
            this.shop = shop;
        }

        @Override
        public void run() {
            while (true) {
                synchronized (lock) {
                    if (flag) {
                        try {
                            lock.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        continue;
                    }
                    if (money >= 5) {
                        shop.sell();
                        money -= 5;
                        flag = true;
                    } else if (money == 0) {
                        System.out.println(name + " 没钱了，回家了");
                        break;
                    } else {
                        System.out.println(name + " 余额不足，等待中...");
                        try {
                            lock.wait(1000);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }
        }
    }
}

改进的地方主要有：

1. 将静态变量 count 和 money 改为实例变量，这样可以支持多个早餐店同时运行。
2. 在 sell() 方法中使用 if 判断代替 while 循环，这样可以避免虚假唤醒问题。
3. 在 Customer 类中加入一个 flag 变量，标记当前顾客是否已经购买，避免重复购买。
4. 将 lock 对象改为实例变量 this，这样可以避免多个早餐店之间的互相干扰。
5. 在 Customer 类中加入了一个 while 循环，避免了顾客在购买之后还未离开店铺就再次购买的情况。同时，使用了 lock.wait() 来等待顾客购买完毕之后再继续购买。