温故知新—-线程之Runnable与Callable接口的本质区别

预备知识：Java中的线程对象是Thread,新建线程也只有通过创建Thread对象的实例来创建。

先说结论

1 Runnable没有返回值的FunctionalInterface(jdk 1.8概念)接口，相反Callable是有返回值的FunctionalInterface接口

2 Runnable + Thread 创建一个无返回结果的任务线程

3 Runnable + Callable +Thread 创建一个有返回结果的任务线程

一：Runnable 示例

创建一个无返回结果的任务线程，so eazy !!!!

public static void main(String[] args) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println(Thread.currentThread().getName() + "我是一个无返回结果的任务线程");
            }
        },"线程一:").start(); //start()开启任务
    }

二：Callable示例

2.1 JAVA异步编程之Callbacks与Futures模型我是用Executors线程池的方式来创建的。

2.2 用最原始的方法

public class PrimitiveCallable implements Callable, Runnable {
    
    public static void main(String[] args) {
        //实现
        new Thread(new PrimitiveCallable(), "线程二:").start();
    }
    @Override
    public void run() {//Runnable实现
        try {
            Object call = this.call();
            System.out.println(call);
        } catch (Exception exception) {
            exception.printStackTrace();
        }
    }
    @Override
    public Object call() throws Exception { //Callable 实现
        return "异步任务返回的结果!!!";
    }
}

2.3 FutureTask 一种jdk的实现方式

public class FutureTask implements RunnableFuture { //RunnableFuture 实现了以上2个接口
    ........省略.........
	public void run() { //重写run实现
        if (state != NEW ||
            !UNSAFE.compareAndSwapObject(this, runnerOffset,
                                         null, Thread.currentThread()))
            return;
        try {
            Callable c = callable; //构建对象是传入的参数
            if (c != null && state == NEW) {
                V result;
                boolean ran;
                try {
                    result = c.call(); //调用任务并返回结果
                    ran = true;
                } catch (Throwable ex) {
                    result = null;
                    ran = false;
                    setException(ex); //设置异常时的结果
                }
                if (ran)
                    set(result); //设置结果
            }
        } finally {
            runner = null;
            int s = state;
            if (s >= INTERRUPTING)
                handlePossibleCancellationInterrupt(s);
        }
    }
     ........省略.........
}

小结

1 不要纠结有几种创建线程的方法了，就一种即通过Thread，但Thread有9个构造函数方法

2 9个构造函数方法

1 public Thread()
2 public Thread(Runnable target)
3 Thread(Runnable target, AccessControlContext acc)
4 public Thread(ThreadGroup group, Runnable target)
5 public Thread(String name)
6 public Thread(ThreadGroup group, String name)
7 public Thread(Runnable target, String name)
8 public Thread(ThreadGroup group, Runnable target, String name)
9 public Thread(ThreadGroup group, Runnable target, String name,
                  long stackSize)

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