说说Runnable与Callable

Callable接口：

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public interface Callable<V> {     V call() throws Exception; }

Runnable接口：

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public interface Runnable {     public abstract void run(); }

相同点：

1. 两者都是接口；
2. 两者都可用来编写多线程程序；
3. 两者都需要调用Thread.start()启动线程；

 

不同点：

1. 两者最大的不同点是：实现Callable接口的任务线程能返回执行结果；而实现Runnable接口的任务线程不能返回结果；
2. Callable接口的call()方法允许抛出异常；而Runnable接口的run()方法的异常只能在内部消化，不能继续上抛；

 

注意点：

• Callable接口支持返回执行结果，此时需要调用FutureTask.get()方法实现，此方法会阻塞主线程直到获取‘将来’结果；当不调用此方法时，主线程不会阻塞！

 

Callable工作的Demo：

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package com.callable.runnable;   import java.util.concurrent.Callable; import java.util.concurrent.ExecutionException; import java.util.concurrent.FutureTask;   /**  * Created on 2016/5/18.  */ public class CallableImpl implements Callable<String> {       public CallableImpl(String acceptStr) {         this.acceptStr = acceptStr;     }       private String acceptStr;       @Override     public String call() throws Exception {         // 任务阻塞 1 秒         Thread.sleep(1000);         return this.acceptStr + " append some chars and return it!";     }         public static void main(String[] args) throws ExecutionException, InterruptedException {         Callable<String> callable = new CallableImpl("my callable test!");         FutureTask<String> task = new FutureTask<>(callable);         long beginTime = System.currentTimeMillis();         // 创建线程         new Thread(task).start();         // 调用get()阻塞主线程，反之，线程不会阻塞         String result = task.get();         long endTime = System.currentTimeMillis();         System.out.println("hello : " + result);         System.out.println("cast : " + (endTime - beginTime) / 1000 + " second!");     } }

　　

测试结果：

 

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hello : my callable test! append some chars and return it! cast : 1 second!   Process finished with exit code 0

　　

Runnable工作的Demo：

 

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package com.callable.runnable;   /**  * Created on 2016/5/18.  */ public class RunnableImpl implements Runnable {       public RunnableImpl(String acceptStr) {         this.acceptStr = acceptStr;     }       private String acceptStr;       @Override     public void run() {         try {             // 线程阻塞 1 秒，此时有异常产生，只能在方法内部消化，无法上抛             Thread.sleep(1000);         } catch (InterruptedException e) {             e.printStackTrace();         }         // 最终处理结果无法返回         System.out.println("hello : " + this.acceptStr);     }         public static void main(String[] args) {         Runnable runnable = new RunnableImpl("my runable test!");         long beginTime = System.currentTimeMillis();         new Thread(runnable).start();         long endTime = System.currentTimeMillis();         System.out.println("cast : " + (endTime - beginTime) / 1000 + " second!");     } }

　　

测试结果：

 

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cast : 0 second! hello : my runable test!   Process finished with exit code 0

　　

写此篇的原因是一次面试中问到Callable与Runnable的区别，当时用的多的是Runnable，而Callable使用很少！

比较了两者后（网上查了不少），发现Callable在很多特殊的场景下还是很有用的！最后留点抄的代码，加深对Callable的认识！

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package com.inte.fork;   /**  * Created on 2016/4/20.  */   import java.util.*; import java.util.concurrent.*;   import static java.util.Arrays.asList;   public class Sums {       static class Sum implements Callable<Long> {         private final long from;         private final long to;           Sum(long from, long to) {             this.from = from;             this.to = to;         }           @Override         public Long call() {             long acc = 0;             for (long i = from; i <= to; i++) {                 acc = acc + i;             }             System.out.println(Thread.currentThread().getName() + " : " + acc);             return acc;         }     }       public static void main(String[] args) throws Exception {         ExecutorService executor = Executors.newFixedThreadPool(3);         List<Future<Long>> results = executor.invokeAll(asList(                 new Sum(0, 10), new Sum(0, 1_000), new Sum(0, 1_000_000)         ));         executor.shutdown();           for (Future<Long> result : results) {             System.out.println(result.get());         }     } }