如何获取线程的返回值？

约定不等于承诺〃 2023-02-20 02:55 205阅读 0赞

## 获取线程的返回值 ##

1.  主线程等待法，主线程调用sleep方法（让主线程去循环等待子线程结束并赋值；缺点：代码臃肿，等待时间无法精准控制；**不推荐使用**）；
2.  使用Thread类的join()阻塞当前线程以等待子线程处理结束（不能精准控制多个线程中的其中一个；**不推荐使用**）；
3.  **通过Callable接口实现call()获取线程返回值（通过FutrueTask Or 线程池获取，推荐使用）**

>  FutrueTask的构造方法可以传入Callable实现类的实例；  
> isDone()可以判断call是否执行结束；  
> get()用来获取线程完成后的返回值；

## 实现 ##

Tips：由于前两种方法都无法精准控制等待时间或者是线程对象，所以对第三种方法进行实现

CallableDemo.java

package Thread;
    
    import java.util.concurrent.Callable;
    
    public class CallableDemo implements Callable<String> {
        
        @Override
        public String call() throws Exception {
        
            String res = "Hello";
            System.out.println("Call ready");
            Thread.currentThread().sleep(5000);
            System.out.println("Call down");
            return res;
        }
    }

### FutureTaskDemo.java（FutrueTask获取线程返回值） ###

package Thread;
    
    
    import java.util.concurrent.ExecutionException;
    import java.util.concurrent.FutureTask;
    
    public class FutureTaskDemo {
        
    
        public static void main(String[] args) throws ExecutionException, InterruptedException {
        
            FutureTask futureTask = new FutureTask(new CallableDemo());
            new Thread(futureTask).start();
            if (!futureTask.isDone()){
        
                System.out.println("Task is not finshed,Please wait");
            }
            System.out.println("Return value is "+futureTask.get());
        }
    }

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### ThreadPoolDemo.java（线程池获取线程返回值） ###

package Thread;
    
    import java.util.concurrent.ExecutionException;
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
    import java.util.concurrent.Future;
    
    public class ThreadPoolDemo {
        
    
        public static void main(String[] args) {
        
            ExecutorService executorService = Executors.newCachedThreadPool();
            Future<String> future= executorService.submit(new CallableDemo());
            if (!future.isDone()){
        
                System.out.println("Task is not finshed,Please wait");
            }
            try {
        
                System.out.println(future.get());
            } catch (InterruptedException e) {
        
                e.printStackTrace();
            } catch (ExecutionException e) {
        
                e.printStackTrace();
            }finally {
        
                executorService.shutdown();
            }
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDE5MDExMw_size_16_color_FFFFFF_t_70 1]

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