java 面试题 -- 线程 按序 交替
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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 ------------------
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