java 面试题 -- 线程按序交替

╰+攻爆jí腚メ 2022-02-04 15:21 160阅读 0赞

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？

package com.company;
    
    import java.util.concurrent.locks.Condition;
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;
    
    /*
     * 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(i);
                }
    
            }, "A").start();
    
            new Thread(() -> {
    
                for (int i = 1; i <= 10; i++) {
                    ad.loopB(i);
                }
    
            }, "B").start();
    
            new Thread(() -> {
    
                for (int i = 1; i <= 10; i++) {
                    ad.loopC(i);
    
                }
    
            }, "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();
    
        /**
         * @param totalLoop : 循环第几轮
         */
        void loopA(int totalLoop) {
            lock.lock();
    
            try {
                //1. 判断
                if (number != 1) {
                    condition1.await();
                }
    
                //2. 打印
                for (int i = 1; i <= 1; i++) {
                    System.out.println(Thread.currentThread().getName() + "\t" + i + "\t" + totalLoop);
                }
    
                //3. 唤醒
                number = 2;
                condition2.signal();
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }
    
        void loopB(int totalLoop) {
            lock.lock();
    
            try {
                //1. 判断
                if (number != 2) {
                    condition2.await();
                }
    
                //2. 打印
                for (int i = 1; i <= 1; i++) {
                    System.out.println(Thread.currentThread().getName() + "\t" + i + "\t" + totalLoop);
                }
    
                //3. 唤醒
                number = 3;
                condition3.signal();
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }
    
        void loopC(int totalLoop) {
            lock.lock();
    
            try {
                //1. 判断
                if (number != 3) {
                    condition3.await();
                }
    
                //2. 打印
                for (int i = 1; i <= 1; i++) {
                    System.out.println(Thread.currentThread().getName() + "\t" + i + "\t" + totalLoop);
                }
                System.out.println("------------------");
                //3. 唤醒
                number = 1;
                condition1.signal();
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }
    
    }

上面有一部分使用java1.8新特性写的，看下结果：

A    1    1
    B    1    1
    C    1    1
    ------------------
    A    1    2
    B    1    2
    C    1    2
    ------------------
    A    1    3
    B    1    3
    C    1    3
    ------------------
    A    1    4
    B    1    4
    C    1    4
    ------------------
    A    1    5
    B    1    5
    C    1    5
    ------------------
    A    1    6
    B    1    6
    C    1    6
    ------------------
    A    1    7
    B    1    7
    C    1    7
    ------------------
    A    1    8
    B    1    8
    C    1    8
    ------------------
    A    1    9
    B    1    9
    C    1    9
    ------------------
    A    1    10
    B    1    10
    C    1    10
    ------------------