Java 多线程 面试题

逆流者 2020年08月04日 67次浏览

1、编写一个程序,开启 3 个线程,这三个线程的 ID 分别为 A、B、C,每个线程将自己的 ID 在屏幕上打印 10 遍,要求输出的结果必须按顺序显示。如:ABCABCABC…… 依次递归。

/*
 * 编写一个程序,开启 3 个线程,这三个线程的 ID 分别为 A、B、C,每个线程将自己的 ID 在屏幕上打印 10 遍,要求输出的结果必须按顺序显示。
 *	如:ABCABCABC…… 依次递归
 */
public class TestABCAlternate {

    public static void main(String[] args) {
        AlternateDemo ad = new AlternateDemo();

        new Thread(() -> {

            for (int i = 1; i <= 10; i++) {
                ad.loopA();
            }

        }, "A").start();

        new Thread(() -> {

            for (int i = 1; i <= 10; i++) {
                ad.loopB();
            }

        }, "B").start();

        new Thread(() -> {

            for (int i = 1; i <= 10; i++) {
                ad.loopC();
            }

        }, "C").start();
    }

}

class AlternateDemo {

    private int number = 1; //当前正在执行线程的标记

    private Lock lock = new ReentrantLock();
    private Condition condition1 = lock.newCondition();
    private Condition condition2 = lock.newCondition();
    private Condition condition3 = lock.newCondition();

    public void loopA() {
        lock.lock();

        try {
            //1. 判断
            if (number != 1) {
                condition1.await();
            }

            //2. 打印
            System.out.print(Thread.currentThread().getName());

            //3. 唤醒
            number = 2;
            condition2.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }

    public void loopB() {
        lock.lock();

        try {
            //1. 判断
            if (number != 2) {
                condition2.await();
            }

            //2. 打印
            System.out.print(Thread.currentThread().getName());

            //3. 唤醒
            number = 3;
            condition3.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }

    public void loopC() {
        lock.lock();

        try {
            //1. 判断
            if (number != 3) {
                condition3.await();
            }

            //2. 打印
            System.out.print(Thread.currentThread().getName());

            //3. 唤醒
            number = 1;
            condition1.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }

}

测试结果:
ABCABCABCABCABCABCABCABCABCABC