Java Callable用法

Callable 和 Runnable 的使用方法大同小异， 区别在于：
1.Callable 使用 call（） 方法， Runnable 使用 run() 方法
2.call() 可以返回值， 而 run()方法不能返回。
3.call() 可以抛出受检查的异常，比如ClassNotFoundException， 而run()不能抛出受检查的异常。
Callable示例如下：

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;
	}
}

public class CallableTest {
	public static void main(String[] args) throws InterruptedException,
			ExecutionException {
		ExecutorService exec = Executors.newCachedThreadPool();
		ArrayList<Future<String>> results = new ArrayList<Future<String>>();	//Future 相当于是用来存放Executor执行的结果的一种容器
		for (int i = 0; i < 10; i++) {
			results.add(exec.submit(new TaskWithResult(i)));
		}
		for (Future<String> fs : results) {
			if (fs.isDone()) {
				System.out.println(fs.get());
			} else {
				System.out.println("Future result is not yet complete");
			}
		}
		exec.shutdown();
	}
}

执行结果

result of TaskWithResult 0
result of TaskWithResult 1
result of TaskWithResult 2
result of TaskWithResult 3
result of TaskWithResult 4
result of TaskWithResult 5
result of TaskWithResult 6
result of TaskWithResult 7
result of TaskWithResult 8
result of TaskWithResult 9

Runnable示例：

public class LiftOff implements Runnable {

	protected int countDown = 10;
	private static int taskCount = 0;
	private final int id = taskCount++;

	public LiftOff() {

	}

	public LiftOff(int countDown) {
		this.countDown = countDown;
	}

	public String status() {
		return "#" + id + "(" + (countDown > 0 ? countDown : "LiftOff! ") + ")";
	}

	@Override
	public void run() {
		while (countDown-- > 0) {
			System.out.print(status());
			Thread.yield();
		}
		System.out.println();
	}

	public static void main(String[] args) {
		ExecutorService exec = Executors.newFixedThreadPool(1);
		for (int i = 0; i < 5; i++) {
			exec.execute(new LiftOff());
		}
		exec.shutdown();
	}
}

执行结果

#0(9)#0(8)#0(7)#0(6)#0(5)#0(4)#0(3)#0(2)#0(1)#0(LiftOff! )
#1(9)#1(8)#1(7)#1(6)#1(5)#1(4)#1(3)#1(2)#1(1)#1(LiftOff! )
#2(9)#2(8)#2(7)#2(6)#2(5)#2(4)#2(3)#2(2)#2(1)#2(LiftOff! )
#3(9)#3(8)#3(7)#3(6)#3(5)#3(4)#3(3)#3(2)#3(1)#3(LiftOff! )
#4(9)#4(8)#4(7)#4(6)#4(5)#4(4)#4(3)#4(2)#4(1)#4(LiftOff! )

注意ExecutorService 在Callable中使用的是submit()， 在Runnable中使用的是 execute()

评论

2 楼 tabsuny 2013-08-13  

       ......
        for (Future<String> fs : results) { 
            if (fs.isDone()) { 
                System.out.println(fs.get()); 
            } else { 
                System.out.println("Future result is not yet complete"); 
            } 
        }
        ......
这个for 是怎么处理的？ 比如fs.get()等待

1 楼 tabsuny 2013-08-13