同步代码实现

package tongbu;

public class JoinDemo {
    public static void main(String[] args) {
        Thread thread = new Thread(() -> {
            System.out.println("你好1");
        });

        Thread thread1 = new Thread(() -> {
            try {
                thread.join();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
            System.out.println("你好2");
        });

        Thread thread2 = new Thread(() -> {
            try {
                thread.join();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
            System.out.println("你好3");
        });

        thread.start();
        thread1.start();
        thread2.start();
    }
}

package tongbu;

import java.util.concurrent.CountDownLatch;

/**
 * @author: dlwlrma
 * @data 2025年05月31日 17:14
 * @Description
 */
public class CountDownLattchDemo {
    public static void main(String[] args) {
        CountDownLatch latch1 = new CountDownLatch(1);
        CountDownLatch latch2 = new CountDownLatch(1);

        Thread thread = new Thread(() -> {
            System.out.println("你好1");
            //释放
            latch1.countDown();
        });

        Thread thread1 = new Thread(() -> {
            try {
                latch1.await();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
            System.out.println("你好2");
            latch2.countDown();
        });

        Thread thread2 = new Thread(() -> {
            try {
                latch2.await();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
            System.out.println("你好3");
        });

        thread.start();
        thread1.start();
        thread2.start();
    }
}

package yibu;

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;

/**
 * @author: dlwlrma
 * @data 2025年05月31日 18:26
 * @Description
 * 任务描述：任务一执行完毕后之后执行任务二，任务三和任务一任务二一起执行，所有任务都有返回值，等任务二和任务三都执行完成后，在执行任务四
 */
public class CompletableFutureDemo {
    public static void main(String[] args) {
        CompletableFuture<String> task1 = CompletableFuture.supplyAsync(()->{
           try {
               Thread.sleep(1000);
           } catch (InterruptedException e) {
               Thread.currentThread().interrupt();
               throw new RuntimeException(e);
           }
           return "任务一已经执行完毕";
        });

        CompletableFuture<String> task2 = task1.handle((res1,Throwable)->{
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
                throw new RuntimeException(e);
            }
            return "任务二已经执行完毕";
        });

        CompletableFuture<String> task3 = CompletableFuture.supplyAsync(()->{
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
                throw new RuntimeException(e);
            }
            return "任务三已经执行完毕";
        });

        //执行第四步
        CompletableFuture<String> task4 = CompletableFuture.allOf(task2,task3).handle((res2,Throwable)->{
            try {
                return "返回结果4" +task2.get() + task3.get();
            } catch (ExecutionException | InterruptedException e) {
                throw new RuntimeException(e);
            }
        });

        String s = task4.join();
        System.out.println(s);
    }
}