public class Clerk {
    private int product = -1;

    public synchronized void setProduct(int product) throws InterruptedException {
        waitIfFull();
        this.product = product;
        System.out.printf("生产者设定 (%d)%n", this.product);
        notify();
    }

    private synchronized void waitIfFull() throws InterruptedException {
        while (this.product != -1) {
            wait();
        }
    }

    public synchronized int getProduct() throws InterruptedException {
        waitIfEmpty();
        int p = this.product;
        this.product = -1;
        System.out.printf("消费者取走 (%d)%n", p);
        notify();
        return p;
    }

    private synchronized void waitIfEmpty() throws InterruptedException {
        while (this.product == -1) {
            wait();
        }
    }
}