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五、Callable 接口

news 2025/9/1 3:33:22

要和 1.6Runnable 和 Thread 类，几种创建线程方式比较。

创建线程几种方式呢？5 种

继承 Thread 类
Runnable 接口
Java 5 后，实现 Callable 接口
Java 线程池
ComplatableFuture

5.1 Callable 和 Runnable 区别

有三个区别：

具体方法不同：一个是run，一个是call
Runnable没有返回值；Callable可以返回执行结果，是个泛型
Callable接口的call()方法允许抛出异常；Runnable的run()方法异常只能在内部消化，不能往上继续抛

FutureTask futureTask = new FutureTask(new Callable());
Thread t = new Thread(FutureTask);
t.start();

Thread t = new Thread(new Runnable());
t.start();

5.2 Callable 创建线程

new Thread()是不接收Callable对象的，只能接收Runnable对象，那到底该如何使用Callable呢？

这时候借助一个FutureTask -> RunnableFuture -> Runnable

所以其实根本上，还是因为它实现了RunnableFuture接口，这个接口继承于Runnable接口

所以肯定是可以运行起来了！

new Thread(new FutureTask<>(new CallableFun()), "Callable").start();

class CallableFun implements Callable<Integer> {@Overridepublic Integer call() throws Exception {Thread.sleep(6);System.out.println(Thread.currentThread().getName() + "Callable is running!");return 666;}
}class RunnableFun implements Runnable {@Overridepublic void run() {try {Thread.sleep(10);} catch (InterruptedException e) {throw new RuntimeException(e);}System.out.println(Thread.currentThread().getName() + "Runnable is running!");}
}public class CallableDemo {public static void main(String[] args) {new Thread(new RunnableFun(), "RunableFun").start();new Thread(new FutureTask<>(new CallableFun()), "Callable").start();}
}

那么如何处理返回值呢？

使用Thread进行过去，发现没有那样的方法

这里使用FutureTask.get进行获取返回值，因为嵌在它里面，也可以理解

public class CallableDemo {public static void main(String[] args) throws ExecutionException, InterruptedException {new Thread(new RunnableFun(), "RunableFun").start();FutureTask<Integer> futureTask = new FutureTask<>(new CallableFun());new Thread(futureTask, "CallableFun").start();System.out.println("获取到结果之前");Integer res = futureTask.get();System.out.println("获取到结果之后" + res);}
}

主线程，在 Callable 执行完之后才打印值，就是等他们执行完才得到返回值，get 方法会阻塞主线程。

因为Callable接口有throw可以处理异常，所以需要抛出去
需要将睡眠时间更改一下

class CallableFun implements Callable<Integer> {@Overridepublic Integer call() throws Exception {Thread.sleep(1000);System.out.println(Thread.currentThread().getName() + " Callable is running!");return 666;}
}class RunnableFun implements Runnable {@Overridepublic void run() {try {Thread.sleep(500);} catch (InterruptedException e) {throw new RuntimeException(e);}System.out.println(Thread.currentThread().getName() + " Runnable is running!");}
}

5.3 FutureTask使用

一个FutureTask对象之后就只有一个结果输出，虽然是两个线程

public static void main(String[] args) throws ExecutionException, InterruptedException {FutureTask<Integer> futureTask = new FutureTask<>(new CallableFun());Thread t1 = new Thread(futureTask, "线程 1");Thread t2 = new Thread(futureTask, "线程 2");t1.start();t2.start();System.out.println("获取到结果之前");Integer res = futureTask.get();System.out.println("获取到结果之后" + res);
}

2 个FutureTask对象之后才会有 2 个结果输出

class CallableFun implements Callable<Integer> {@Overridepublic Integer call() throws Exception {Thread.sleep(500);System.out.println(Thread.currentThread().getName() + " Callable is running!");return new Random().nextInt(1000);}
}public static void main(String[] args) throws ExecutionException, InterruptedException {FutureTask<Integer> futureTask1 = new FutureTask<>(new CallableFun());FutureTask<Integer> futureTask2 = new FutureTask<>(new CallableFun());Thread t1 = new Thread(futureTask1, "线程 1");Thread t2 = new Thread(futureTask2, "线程 2");t1.start();t2.start();System.out.println("获取到结果之前");Integer res1 = futureTask1.get();Integer res2 = futureTask2.get();System.out.println("获取到结果之后" + res1);System.out.println("获取到结果之后" + res2);
}

FutureTask的方法

get：阻塞主线程
isDone：判断异步线程是否执行完毕
isCancelled：是否被取消了
cancel

- true：打断子线程执行，并且抛出异常，无返回结果
- false：不打断子线程执行，并且抛出异常，无返回结果

isDone方法：就是另一种判断是否get完成的方法

class CallableFun implements Callable<Integer> {@Overridepublic Integer call() throws Exception {for (int i = 0; i < 10; i++) {Thread.sleep(500);System.out.println(Thread.currentThread().getName() + " Callable is running!");}return new Random().nextInt(1000);}
}public class CallableDemo {public static void main(String[] args) throws ExecutionException, InterruptedException {FutureTask<Integer> futureTask = new FutureTask<>(new CallableFun());new Thread(futureTask, "线程 1").start();System.out.println();;System.out.println("get 前：" + futureTask.isDone());Integer res = futureTask.get();System.out.println("get 后：" + futureTask.isDone());System.out.println("获取到结果：" + res);}
}

isCancelled、cancel方法

这里Thread.sleep是为了让主线程睡眠，子线程继续执行futureTask任务，来判断是否让子线程继续执行。

package CallableInter;import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;class CallableFun implements Callable<Integer> {@Overridepublic Integer call() throws Exception {for (int i = 0; i < 10; i++) {Thread.sleep(500);System.out.println(Thread.currentThread().getName() + " Callable is running!");}return new Random().nextInt(1000);}
}public class CallableDemo {public static void main(String[] args) throws ExecutionException, InterruptedException {//        new Thread(new RunnableFun(), "RunableFun").start();FutureTask<Integer> futureTask = new FutureTask<>(new CallableFun());new Thread(futureTask, "线程 1").start();System.out.println("get 前是否 Done：" + futureTask.isDone());System.out.println("get 前取消：" + futureTask.isCancelled());Thread.sleep(3000);futureTask.cancel(false);Integer res = futureTask.get();System.out.println("get 后取消：" + futureTask.isCancelled());System.out.println("get 后是否 Done：" + futureTask.isDone());System.out.println("获取到结果：" + res);}
}

false不打断子线程的执行，会执行结束