Java 获取多线程返回值的几种方式

第一种：使用Callable加上FutureTask来实现

public static void main(String[] args) throws ExecutionException, InterruptedException {
          
   
        FutureTask<Integer> futureTask=new FutureTask(new TestA());
        Thread thread=new Thread(futureTask);
        thread.start();
        Integer integer = futureTask.get();
        System.out.println(integer);
    }

    static class TestA implements Callable<Object>{
          
   

        @Override
        public Integer call() throws Exception {
          
   
            Thread.sleep(1000);
            return 1;
        }
    }

Callable的call方法已经规定线程的返回值了，很好理解 第二种：主线程等待，直到子线程执行完成

public static void main(String[] args) throws InterruptedException {
          
   
        ThreadTest threadTest=new ThreadTest();
        threadTest.start();
        while (threadTest.a==null){
          
   
            Thread.sleep(100);
        }
        System.out.println(threadTest.a);
    }

    static class ThreadTest extends Thread{
          
   
        Integer a;
        @Override
        public void run() {
          
   
            super.run();
            try {
          
   
                Thread.sleep(1000);
            } catch (InterruptedException e) {
          
   
                e.printStackTrace();
            }
            a=1;
        }
    }

第三种：与第二种类似采用Thread的join方法，主线程会等调用了join的子线程执行完后再执行

public static void main(String[] args) throws InterruptedException {
          
   
        ThreadTest threadTest=new ThreadTest();
        threadTest.start();
        threadTest.join();
        System.out.println(threadTest.a);
    }
    static class ThreadTest extends Thread{
          
   
        Integer a;
        @Override
        public void run() {
          
   
            super.run();
            try {
          
   
                Thread.sleep(1000);
            } catch (InterruptedException e) {
          
   
                e.printStackTrace();
            }
            a=1;
        }
    }

第四种：使用CountDownLatch，CountDownLatch的await方法表示等待，countDown方法表示等待线程数减一，当等待线程数为0时，开始向下执行

public static void main(String[] args) throws InterruptedException {
          
   
        CountDownLatch countDownLatch=new CountDownLatch(1);
        ThreadTest02 threadTest02=new ThreadTest02(countDownLatch);
        threadTest02.start();
        countDownLatch.await();
        System.out.println(threadTest02.a);
    }
   static class ThreadTest02 extends Thread{
          
   

        private CountDownLatch countDownLatch;
        private int a;
        public ThreadTest02(CountDownLatch countDownLatch){
          
   
            this.countDownLatch=countDownLatch;
        }

       @Override
       public void run() {
          
   
           super.run();
           try {
          
   
               Thread.sleep(1000);
               a=1;
           } catch (InterruptedException e) {
          
   
               e.printStackTrace();
           }
           countDownLatch.countDown();
       }
   }