P1115_PrintFoobarAlternately.java

package yyl.leetcode.p11;

/**
 * <h3>交替打印FooBar</h3><bre> 我们提供一个类：
 * 
 * <pre>
 * class FooBar {
 *     public void foo() {
 *         for (int i = 0; i < n; i++) {
 *             print("foo");
 *         }
 *     }
 * 
 *     public void bar() {
 *         for (int i = 0; i < n; i++) {
 *             print("bar");
 *         }
 *     }
 * }
 * </pre>
 * 
 * 两个不同的线程将会共用一个 FooBar 实例。其中一个线程将会调用 foo() 方法，另一个线程将会调用 bar() 方法。<bre> 请设计修改程序，以确保 "foobar" 被输出 n 次。<bre>
 * 
 * <pre>
 * 示例 1:
 * 输入: n = 1
 * 输出: "foobar"
 * 解释: 这里有两个线程被异步启动。其中一个调用 foo() 方法, 另一个调用 bar() 方法，"foobar" 将被输出一次。
 * 
 * 示例 2:
 * 输入: n = 2
 * 输出: "foobarfoobar"
 * 解释: "foobar" 将被输出两次。
 * </pre>
 */
public class P1115_PrintFoobarAlternately {

    public static void main(String[] args) {
        Runnable printFoo = () -> System.out.print("foo");
        Runnable printBar = () -> System.out.print("bar");
        FooBar sample = new FooBar(2);
        new Thread(() -> {
            try {
                sample.foo(printFoo);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }).start();
        new Thread(() -> {
            try {
                sample.bar(printBar);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }).start();
    }

    static class FooBar {

        private final int n;
        private Object lock = new Object();
        private int signal = 0;

        public FooBar(int n) {
            this.n = n;
        }

        public void foo(Runnable printFoo) throws InterruptedException {
            for (int i = 0; i < n; i++) {
                synchronized (lock) {
                    while (signal != 0) {
                        lock.wait();
                    }
                    // printFoo.run() outputs "foo". Do not change or remove this line.
                    printFoo.run();
                    signal = 1;
                    lock.notifyAll();
                }
            }
        }

        public void bar(Runnable printBar) throws InterruptedException {
            for (int i = 0; i < n; i++) {
                synchronized (lock) {
                    while (signal != 1) {
                        lock.wait();
                    }
                    // printBar.run() outputs "bar". Do not change or remove this line.
                    printBar.run();
                    signal = 0;
                    lock.notifyAll();
                }
            }
        }
    }
}