（黑马Java多线程与并发库高级应用）10 Java5线程并发库的应用

Future 表示异步计算的结果。它提供了检查计算是否完成的方法，以等待计算的完成，并获取计算的结果。计算完成后只能使用 get 方法来获取结果，如有必要，计算完成前可以阻塞此方法。取消则由 cancel 方法来执行。还提供了其他方法，以确定任务是正常完成还是被取消了。一旦计算完成，就不能再取消计算。如果为了可取消性而使用 Future 但又不提供可用的结果，则可以声明 Future<?> 形式类型、并返回 null 作为底层任务的结果。

用法示例（注意，下列各类都是构造好的。）

 

 interface ArchiveSearcher { String search(String target); }
 class App {
   ExecutorService executor = ...
   ArchiveSearcher searcher = ...
   void showSearch(final String target)
       throws InterruptedException {
     Future<String> future
       = executor.submit(new Callable<String>() {
         public String call() {
             return searcher.search(target);
         }});
     displayOtherThings(); // do other things while searching
     try {
       displayText(future.get()); // use future
     } catch (ExecutionException ex) { cleanup(); return; }
   }
 }

package cn.itcast.heima2;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class CallableAndFuture {

    public static void main(String[] args) throws InterruptedException, ExecutionException {
        ExecutorService threadPool = Executors.newSingleThreadExecutor();
        Future<String> future = threadPool.submit(new Callable<String>() {

            @Override
            public String call() throws Exception {
                Thread.sleep(2000);
                return "hello";
            }
        });
        
        System.out.println("等待结果");
        System.out.println("拿到结果"+future.get());
    }

}

 

 

package cn.itcast.heima2;

import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.CompletionService;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorCompletionService;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class CallableAndFuture {

    static Random rd = new Random();

    public static void main(String[] args) throws InterruptedException, ExecutionException {
        ExecutorService threadPool = Executors.newSingleThreadExecutor();
        Future<String> future = threadPool.submit(new Callable<String>() {

            @Override
            public String call() throws Exception {
                Thread.sleep(2000);
                return "hello";
            }
        });

        System.out.println("等待结果");
        System.out.println("拿到结果" + future.get());

        ExecutorService threadPool2 = Executors.newFixedThreadPool(10);
        CompletionService<Integer> cs = new ExecutorCompletionService<>(threadPool2);
        for (int i = 1; i <= 10; i++) {
            final int seq = i;
            cs.submit(new Callable<Integer>() {

                @Override
                public Integer call() throws Exception {
                    Thread.sleep(rd.nextInt(5000));
                    return seq;
                }
            });
        }
        for(int i=0;i<10;i++){
            System.out.println(cs.take().get());
        }
    }

}