FutureTask获取结果;
3、自己单独声明线程运行,跟第2点类似,FutureTask本身就是个Runnabel实现类,自然可以做为参数传入Thread运行;
那么我们把自定义的Runnable、Callable实现类做为参数构造FutureTask后,FuttureTask是如何运行的呢,我们可以看下FuttureTask中具体的代码实现
//你传入的Runnable与Callable实现类都会在构造函数中转化为Callable
private Callable<V> callable;
public void run() {
if (state != NEW ||
!UNSAFE.compareAndSwapObject(this, runnerOffset,
null, Thread.currentThread()))
return;
try {
Callable<V> c = callable;//你传入的实现类
if (c != null && state == NEW) {
V result;//返回值
boolean ran;
try {
result = c.call();//运行后返回结果
ran = true;
} catch (Throwable ex) {
result = null;
ran = false;
setException(ex);
}
if (ran)
set(result);
}
} finally {
// runner must be non-null until state is settled to
// prevent concurrent calls to run()
runner = null;
// state must be re-read after nulling runner to prevent
// leaked interrupts
int s = state;
if (s >= INTERRUPTING)
handlePossibleCancellationInterrupt(s);
}
}
可以看到FutureTask类本身的run方法,就是执行Runnable、Callable的实现类并获取返回结果的过程。
所以ExecutorService接口中submit方法归根结底还是要把你传入的对象封装成FutureTask对象,并通过FutureTask类的内部实现来获取结果的,返回的Future接口对象也要依赖于FutureTask实例化的,所以无论是直接传入自己的Runnable、Callable实现类还是构建FutureTask传入,本质上都是通过FutureTask去实现,没有什么区别;
以上就是对Future与FutureTask两者关系的一个大致的介绍与分析,其中如有不足与不正确的地方还望指出与海涵。