一、简单使用

Runnable是执行工作的独立任务，但是它不返回任何值。如果你希望任务完成的时能够返回一个值，那么可以实现一个Callable接口。在Java SE5中引入的Callable是一种具有类型参数的泛型，它的类型参数表示的是从call()方法中返回的值，并且必须用ExecutorService.submit()方法调用它。下面是一个简单的例子（摘自Java编程思想）

class TaskWithResult implements Callable
    
      {    private int id;    public TaskWithResult(int id) {        this.id = id;    }    @Override    public String call() throws Exception {        return "Result of TaskWithResult" + id;    }}public class CallableDemo {    public static void main(String[] args) {        ExecutorService executorService = Executors.newCachedThreadPool();        ArrayList
     
      
       > results = new ArrayList<>();        for (int i = 0;i<10;i++){            results.add(executorService.submit(new TaskWithResult(i)));        }        for (Future
       
         f: results){            try {                System.out.println(f.get());            } catch (InterruptedException e) {                e.printStackTrace();            } catch (ExecutionException e) {                e.printStackTrace();            }finally {                executorService.shutdown();            }        }    }}
       
      
     
    

执行的结果如下

Result of TaskWithResult0Result of TaskWithResult1Result of TaskWithResult2Result of TaskWithResult3Result of TaskWithResult4Result of TaskWithResult5Result of TaskWithResult6Result of TaskWithResult7Result of TaskWithResult8Result of TaskWithResult9

二、计算斐波那契数字的数值总和

public class FibonacciSumDemo {    public static void main(String[] args) {        ExecutorService exec = Executors.newCachedThreadPool();        ArrayList
    
     
      > results = new ArrayList
      
       
        >();        for (int i = 1; i <= 6; i++) results.add(exec.submit(new FibonacciSum(i)));        Thread.yield();        exec.shutdown();        for (Future
        
          fi : results)            try {                System.out.println(fi.get());            } catch (Exception e) {                e.printStackTrace();            }    }}class FibonacciSum implements Generator
         
          , Callable
          
            { private int count; private final int n; public FibonacciSum(int n) { this.n = n; } public Integer next() { return fib(count++); } private int fib(int n) { if (n < 2) return 1; return fib(n - 2) + fib(n - 1); } public Integer call() { int sum = 0; for (int i = 0; i < n; i++) sum += next(); return sum; }}
          
         
        
       
      
     
    

Generator接口定义如下

public interface Generator
    
      {    T next();}
    

执行结果如下：

12471220