//Runnable是執行工作的獨立任務，但是它不返回任何值。在Java SE5中引入的Callable是一種具有型別引數的泛型，它的型別引數表的是從方法call()中返回的值，並且必須使用ExecutorServices.submit()方法呼叫它，下面是一個簡單示例。

package com.test;

import java.util.ArrayList;
import java.util.List;
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 CallableTest {
    public static void main(String[] args) {
        ExecutorService exec=Executors.newCachedThreadPool();
        List<Future<String>> results=new
 
 ArrayList<Future<String>>();
        
        for(int i=0;i<5;i++) {
            results.add(exec.submit(new TaskWithResult(i)));
        }
        
        for(Future<String> fs :results) {
            try {
                System.out.println(fs.get());
            } catch (InterruptedException e) {
                e.printStackTrace();
            } 
 
catch (ExecutionException e) {
                e.printStackTrace();
            }
        }
    }
}

class TaskWithResult implements Callable<String> {
    private int id;
    public TaskWithResult(int id) {
        this.id=id;
    }
    
    @Override
    public String call() throws Exception {
        return "result of TaskWithResult "+id;
    }
}