Runnable,Callable,Thread,Future,FutureTask关系

    /**
     * When an object implementing interface <code>Runnable</code> is used
     * to create a thread, starting the thread causes the object‘s
     * <code>run</code> method to be called in that separately executing
     * thread.
     * <p>
     * The general contract of the method <code>run</code> is that it may
     * take any action whatsoever.
     *
     * @see     java.lang.Thread#run()
     */
    public abstract void run();
}

public interface Callable<V> {/**
     * Computes a result, or throws an exception if unable to do so.
     *
     * @return computed result
     * @throws Exception if unable to compute a result
     */
    V call() throws Exception;
}

由代码可以清晰看出：两个接口的差别：Runnable只有一个run()函数，没有返回值；Callable一个泛型接口，call()函数返回的类型就是客户程序传递进来的V类型。

使用实例：

Runnable():

class RunThread implements Runnable

{

	@Override

	public void run()

	{

	}

}

//调用

new thread(new RunThread()).start();

Callable<T>():

class CallThread implements Callable<String>

{

	@Override

	public String call() throws Exception {

		return null;

	}	

}

//调用

ExecutorService pool = Executors.newCachedThreadPool();

Future<String> future = pool.submit(new CallThread());

String result = future.get();//注意这里要加上try_catch异常控制语句

pool.shutdown();

Future:

public interface Future<V> {/**
     * Attempts to cancel execution of this task.  This attempt will
     */boolean cancel(boolean mayInterruptIfRunning);

    /**
     * Returns <tt>true</tt> if this task was cancelled before it complete
     */boolean isCancelled();

    /**
     * Returns <tt>true</tt> if this task completed.
     */boolean isDone();

    /**
     * Waits if necessary for the computation to complete, and then
     */
    V get() throws InterruptedException, ExecutionException;

    /**
     * Waits if necessary for at most the given time for the computation
     * to complete, and then retrieves its result, if available.
     */
    V get(long timeout, TimeUnit unit)
        throws InterruptedException, ExecutionException, TimeoutException;
}

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isDone()，以等待计算的完成，并检索计算的结果。Future的cancel()方法可以取消任务的执行，它有一布尔参数，参数为 true 表示立即中断任务的执行，参数为 false 表示允许正在运行的任务运行完成。Future的 get() 方法等待计算完成，获取计算结果；

public class FutureTask<V> implements RunnableFuture<V>

public interface RunnableFuture<V> extends Runnable, Future<V> {/**
     * Sets this Future to the result of its computation
     * unless it has been cancelled.
     */void run();
}