详解JDK中ExecutorService与Callable和Future对线程的支持

详解JDK中ExecutorService与Callable和Future对线程的支持

1、代码背景：

    假如有Thread1、Thread2、Thread3、Thread4四条线程分别统计C、D、E、F四个盘的大小，所有线程都统计完毕交给Thread5线程去做汇总，应当如何实现？

2、代码：

    统计“盘子”大小的代码，此处实现jdk中的Callable接口，

package com.wang.test.concurrent; 
 
import java.util.concurrent.Callable; 
 
public class Task1 implements Callable { 
 
  private int x; 
  private int y; 
   
  public Task1(int x, int y) { 
    this.x = x; 
    this.y = y; 
  } 
 
  @Override 
  public Integer call() throws Exception { 
    return x*y; 
  } 
 
} 

    统计汇总的代码，也是实现jdk中的Callable接口，

package com.wang.test.concurrent; 
 
import java.util.concurrent.Callable; 
 
public class Task2 implements Callable { 
 
  private int x; 
  private int y; 
  private int q; 
  private int w; 
   
  public Task2(int x, int y, int q, int w) { 
    this.x = x; 
    this.y = y; 
    this.q = q; 
    this.w = w; 
  } 
 
  @Override 
  public Integer call() throws Exception { 
    return x + y + q + w; 
  } 
 
} 

     客户端：使用JDK中Executors.newFixedThreadPool方法创建ExecutorService，ExecutorService的submit方法接收Callable接口的实现，JDK内部将弄成线程处理，使用Future接收submit方法的返回值，当future调用get方法时，如果线程还没有执行完，程序阻塞在这里，知道线程执行完。

package com.wang.test.concurrent; 
 
import java.util.concurrent.ExecutorService; 
import java.util.concurrent.Executors; 
import java.util.concurrent.Future; 
 
public class Client { 
 
  public static void main(String[] args) throws Exception { 
    ExecutorService pool = Executors.newFixedThreadPool(4); 
 
    Task1 t1 = new Task1(1,2); 
    Task1 t2 = new Task1(23,34); 
    Task1 t3 = new Task1(23,456); 
    Task1 t4 = new Task1(3,33); 
    Future f1 = pool.submit(t1); 
    Future f2 = pool.submit(t2); 
    Future f3 = pool.submit(t3); 
    Future f4 = pool.submit(t4); 
     
    //Future调用get方法时，如果线程还没有执行完，程序阻塞在这里 
    Task2 t5 = new Task2(f1.get(), f2.get(), f3.get(), f4.get()); 
    Future f5 = pool.submit(t5); 
     
    System.out.println(f5.get()); 
     
    pool.shutdown(); 
  } 
} 

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