用java解决哲学家就餐问题，使用wait方法

哲学家就餐问题是一个经典的并发问题，可以用Java的wait()方法来实现。

首先，我们需要定义哲学家和筷子的对象。哲学家对象需要维护当前拿到的筷子数量，以及在就餐时需要等待的筷子数量。筷子对象需要维护当前是否被占用。

然后，在哲学家的run方法中，使用synchronized关键字对筷子对象进行加锁。如果当前哲学家拿到的筷子数量不足2个，则需要等待其他哲学家归还筷子。使用wait()方法使线程暂停，直到其他线程调用notify()方法唤醒它。

在哲学家开始就餐时，需要将占用的筷子数量加1，并释放占用的锁。在哲学家就餐结束时，需要将占用的筷子数量减1，并且唤醒等待的其他哲学家继续尝试获取筷子。

下面是一个简单的Java代码示例：

public class Philosopher implements Runnable {
    private int id;
    private Chopstick leftChopstick;
    private Chopstick rightChopstick;
    private int eatCount;

    public Philosopher(int id, Chopstick leftChopstick, Chopstick rightChopstick) {
        this.id = id;
        this.leftChopstick = leftChopstick;
        this.rightChopstick = rightChopstick;
    }

    public void run() {
        try {
            while (eatCount < 3) {
                synchronized (leftChopstick) {
                    while (leftChopstick.isTaken()) {
                        leftChopstick.wait();
                    }
                    leftChopstick.take();
                    System.out.println("Philosopher " + id + " took left chopstick.");
                    synchronized (rightChopstick) {
                        while (rightChopstick.isTaken()) {
                            rightChopstick.wait();
                        }
                        rightChopstick.take();
                        System.out.println("Philosopher " + id + " took right chopstick.");
                        System.out.println("Philosopher " + id + " is eating.");
                        eatCount++;
                        rightChopstick.drop();
                        rightChopstick.notify();
                    }
                    leftChopstick.drop();
                    leftChopstick.notify();
                }
            }
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            return;
        }
    }
}

public class Chopstick {
    private boolean taken;

    public synchronized void take() {
        taken = true;
    }

    public synchronized void drop() {
        taken = false;
    }

    public synchronized boolean isTaken() {
        return taken;
    }
}

public class DiningPhilosophers {
    public static void main(String[] args) throws Exception {
        int numPhilosophers = 5;
        Philosopher[] philosophers = new Philosopher[numPhilosophers];
        Chopstick[] chopsticks = new Chopstick[numPhilosophers];

        for (int i = 0; i < numPhilosophers; i++) {
            chopsticks[i] = new Chopstick();
        }

        for (int i = 0; i < numPhilosophers; i++) {
            philosophers[i] = new Philosopher(i, chopsticks[i], chopsticks[(i + 1) % numPhilosophers]);
            new Thread(philosophers[i]).start();
        }
    }
}