控制三个线程按顺序交替输出数字123123…

synchronized（配合专用锁对象）

通过共享锁和 volatile 变量控制执行顺序，每个线程按指定顺序打印指定内容，确保输出序列如 “123123…”。使用 synchronized 和 wait/notifyAll 实现线程间协作。

/*** AlternateOutput类用于实现三个线程交替输出数字的功能* 通过使用synchronized关键字和wait/notify机制，确保三个线程按照1->2->3的顺序循环输出*/
public class AlternateOutput {/*** 用于线程同步的锁对象*/private static final Object lock = new Object();/*** 当前应该执行的线程编号*/private static int currentThreadNum = 1;/*** 每个线程需要执行的循环次数*/private static final int MAX_LOOP = 10;/*** 线程执行的任务方法，负责按照指定顺序输出内容* @param curThreadNum 当前线程的编号，用于判断是否轮到当前线程执行* @param nextThreadNum 下一个应该执行的线程编号，执行完当前任务后更新此值* @param output 当前线程需要输出的内容*/private static void runTask(int curThreadNum, int nextThreadNum, String output) {// 循环执行指定次数的任务for (int i = 0; i < AlternateOutput.MAX_LOOP; i++) {// 使用synchronized块确保线程安全synchronized (lock) {// 等待直到轮到当前线程执行while (AlternateOutput.currentThreadNum != curThreadNum) {try {lock.wait();} catch (InterruptedException e) {Thread.currentThread().interrupt();return;}}// 输出当前线程的内容System.out.print(output);// 更新下一个应该执行的线程编号currentThreadNum = nextThreadNum;// 唤醒所有等待的线程lock.notifyAll();}}}/*** 程序入口点，创建并启动三个线程实现交替输出* @param args 命令行参数*/public static void main(String[] args) {// 创建第一个线程，负责输出"1"Thread t1 = new Thread(() -> {runTask(1, 2, "1");});t1.start();// 创建第二个线程，负责输出"2"Thread t2 = new Thread(() -> {runTask(2, 3, "2");});t2.start();// 创建第三个线程，负责输出"3"Thread t3 = new Thread(() -> {runTask(3, 1, "3");});t3.start();// 等待所有线程执行完成try {t1.join();t2.join();t3.join();} catch (InterruptedException e) {Thread.currentThread().interrupt();}}
}

ReentrantLock和Condition

通过ReentrantLock和Condition控制执行顺序，确保按1→2→3循环打印10次。每个线程等待其编号轮次，执行打印后唤醒下一个线程。

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;public class PrintNumber {public static final int MAX_LOOP = 10;public static int currentNum = 1;public static final ReentrantLock lock = new ReentrantLock();public static final Condition c1 = lock.newCondition();public static final Condition c2 = lock.newCondition();public static final Condition c3 = lock.newCondition();public static void main(String[] args) {Thread t1 = new Thread(new PrintNumberTask(1));Thread t2 = new Thread(new PrintNumberTask(2));Thread t3 = new Thread(new PrintNumberTask(3));t1.start();t2.start();t3.start();}
}

import java.util.concurrent.locks.Condition;public class PrintNumberTask implements Runnable {private int number;public PrintNumberTask(int num) {this.number = num;}private void printAndSwith(String output, int nextNum, Condition awaitCondition, Condition signalCondition)throws InterruptedException {while (PrintNumber.currentNum != this.number) {awaitCondition.await();}System.out.print(output);PrintNumber.currentNum = nextNum;signalCondition.signal();}@Overridepublic void run() {for (int i = 0; i < PrintNumber.MAX_LOOP; i++) {PrintNumber.lock.lock();try {switch (number) {case 1:printAndSwith("1", 2, PrintNumber.c1, PrintNumber.c2);break;case 2:printAndSwith("2", 3, PrintNumber.c2, PrintNumber.c3);break;case 3:printAndSwith("3", 1, PrintNumber.c3, PrintNumber.c1);break;default:break;}} catch (Exception e) {e.printStackTrace();} finally {PrintNumber.lock.unlock();}}}
}