Callable接口和Runnable接口

Callable接口和Runnable接口相似，区别就是Callable需要实现call方法，而Runnable需要实现run方法；并且，call方法有返回值。

 

Runnable是执行工作的独立任务，不具有返回值。在Java SE5中引入的Callable是一种具有；类型参数的泛型，参数类型为从方法call()中返回的值，并且必须使用ExecutorService.submit()调用它。

Runnable和Callable都是接口
不同之处：
1.Callable可以返回一个类型V，而Runnable不可以
2.Callable能够抛出checked exception,而Runnable不可以。
Callable的源码如下：

public interface Callable {
    /**
     * 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;
}

Runnable的源码如下：

public interface Runnable {
    /**
     * When an object implementing interface Runnable is used
     * to create a thread, starting the thread causes the object's
     * run method to be called in that separately executing
     * thread.
     * 

     * The general contract of the method run is that it may
     * take any action whatsoever.
     *
     * @see     java.lang.Thread#run()
     */
    public abstract void run();
}

案例：

import java.util.*;
import java.util.concurrent.*;

public class CallableDemo {
	
	public static void main(String[] args) {
		ExecutorService exec = Executors.newCachedThreadPool();
		ArrayList> listResult = new ArrayList>();
		
		for (int i = 0; i < 5; i++) {
			listResult.add(exec.submit(new Calls(i)));
		}
		
		for(Future fs:listResult)
			try {
				System.out.println(fs.get());
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			} catch (ExecutionException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
	}

}
class Calls implements Callable{

	private int id;
	public Calls() {
	}
	public Calls(int id) {
		this.id = id;
	}
	@Override
	public String call() throws Exception {
		// TODO Auto-generated method stub
		return "the current id is: "+this.id;
	}
}