1、在子线程中通过join()方法指定顺序
通过join()方法使当前线程“阻塞”，等待指定线程执行完毕后继续执行。
举例：在线程thread2中，加上一句thread1.join()，其意义在于，当前线程2运行到此行代码时会进入阻塞状态，直到线程thread1执行完毕后，线程thread2才会继续运行，这就保证了线程thread1与线程thread2的运行顺序。
public class ThreadJoinDemo { public static void main(String[] args) throws InterruptedException { final Thread thread1 = new Thread(new Runnable() { @Override public void run() { System.out.println("打开冰箱！"); } }); final Thread thread2 = new Thread(new Runnable() { @Override public void run() { try { thread1.join(); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("拿出一瓶牛奶！"); } }); final Thread thread3 = new Thread(new Runnable() { @Override public void run() { try { thread2.join(); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("关上冰箱！"); } }); //下面三行代码顺序可随意调整，程序运行结果不受影响，因为我们在子线程中通过“join()方法”已经指定了运行顺序。 thread3.start(); thread2.start(); thread1.start(); } }
运行结果：
打开冰箱！ 拿出一瓶牛奶！ 关上冰箱！
2、在主线程中通过join()方法指定顺序
简单说一下子线程与主线程的区别，子线程指的是发生在Thread内部的代码，主线程指的是发生在main函数中的代码，我们可以在main函数中通过join()方法让主线程阻塞等待以达到指定顺序执行的目的。
public class ThreadMainJoinDemo { public static void main(String[] args) throws InterruptedException { final Thread thread1 = new Thread(new Runnable() { @Override public void run() { System.out.println("打开冰箱！"); } }); final Thread thread2 = new Thread(new Runnable() { @Override public void run() { System.out.println("拿出一瓶牛奶！"); } }); final Thread thread3 = new Thread(new Runnable() { @Override public void run() { System.out.println("关上冰箱！"); } }); thread1.start(); thread1.join(); thread2.start(); thread2.join(); thread3.start(); } }
基础就不介绍了，多线程系列我博客教程写了很多了，这里推荐大家看看吧：https://www.javastack.cn/categories/Java/
输出结果：
打开冰箱！ 拿出一瓶牛奶！ 关上冰箱！
3、通过倒数计时器CountDownLatch实现
CountDownLatch通过计数器提供了更灵活的控制，只要检测到计数器为0当前线程就可以往下执行而不用管相应的thread是否执行完毕。
public class ThreadCountDownLatchDemo { private static CountDownLatch countDownLatch1 = new CountDownLatch(1); private static CountDownLatch countDownLatch2 = new CountDownLatch(1); public static void main(String[] args) { final Thread thread1 = new Thread(new Runnable() { @Override public void run() { System.out.println("打开冰箱！"); countDownLatch1.countDown(); } }); final Thread thread2 = new Thread(new Runnable() { @Override public void run() { try { countDownLatch1.await(); System.out.println("拿出一瓶牛奶！"); countDownLatch2.countDown(); } catch (InterruptedException e) { e.printStackTrace(); } } }); final Thread thread3 = new Thread(new Runnable() { @Override public void run() { try { countDownLatch2.await(); System.out.println("关上冰箱！"); } catch (InterruptedException e) { e.printStackTrace(); } } }); //下面三行代码顺序可随意调整，程序运行结果不受影响 thread3.start(); thread1.start(); thread2.start(); } }
输出结果：
打开冰箱！ 拿出一瓶牛奶！ 关上冰箱！
4、通过创建单一化线程池newSingleThreadExecutor()实现
单线程化线程池(newSingleThreadExecutor)的优点，串行执行所有任务。
public class ThreadPoolDemo { static ExecutorService executorService = Executors.newSingleThreadExecutor(); public static void main(String[] args) { final Thread thread1 = new Thread(new Runnable() { @Override public void run() { System.out.println("打开冰箱！"); } }); final Thread thread2 =new Thread(new Runnable() { @Override public void run() { System.out.println("拿出一瓶牛奶！"); } }); final Thread thread3 = new Thread(new Runnable() { @Override public void run() { System.out.println("关上冰箱！"); } }); executorService.submit(thread1); executorService.submit(thread2); executorService.submit(thread3); executorService.shutdown(); //使用完毕记得关闭线程池 } }
输出结果：
打开冰箱！ 拿出一瓶牛奶！ 关上冰箱！
来源：blog.csdn.net/jqc874789596/article/details/100557300
