Java 中的 Callable 对象

public interface Callable
   

A task that returns a result and may throw an exception. Implementors define a single method with no arguments called call.

The Callable interface is similar to Runnable, in that both are designed for classes whose instances are potentially executed by another thread. A Runnable, however, does not return a result and cannot throw a checked exception.

The Executors(An object that executes submitted Runnable tasks) class contains utility(有多种用途的) methods to convert from other common forms to Callable classes.

方法：

V call() throws Exception

下面来比较 Callable 和 Runnable 接口：

Callable是类似于Runnable的接口，实现Callable接口的类和实现Runnable的类都是可被其它线程执行的任务。
Callable和Runnable有几点不同：
（1）Callable规定的方法是call()，而Runnable规定的方法是run().
（2）Callable的任务执行后可返回值，而Runnable的任务是不能返回值的。
（3）call()方法可抛出异常，而run()方法是不能抛出异常的。
（4）运行Callable任务可拿到一个Future(A Future represents the result of an asynchronous computation.)对象， 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，并检索计算的结果。通过Future对象可了解任务执行情况，可取消任务的执行，还可获取任务执行的结果。

运用Callable，如：

public class BatteryTask  implements Callable
  
   {
    private Context context;
    private Battery battery;
    
    public BatteryTask(Context context,Battery battery){
        this.context = context;
        this.battery = battery;
    }
    @Override
    public Result call() throws Exception {
        try{...return...
  

............

Callback
  
    callback = BatteryAlarmReceiver.this;
ExecutorService service = Executors.newSingleThreadExecutor();
Future
   
     future = null; BatteryTask task = new BatteryTask(context); future = service.submit(task); String result = null; if (null != future) { result = future.get(); }... ...