关于java:线程之ThreadRunnableCallable

通常创立线程应用两种形式
1.继承Thread类,重写run办法

public class ThreadDemo extends Thread {

    @Override
    public void run() {
        System.out.println("创立线程形式1");
    }

    public static void main(String[] args) {
        ThreadDemo threadDemo = new ThreadDemo();
        threadDemo.start();
    }
    
}

2.实现Runnable接口(Runnbale中只有一个run办法),重写run办法。而后把实例作为参数传入Thread的构造方法中

public class ThreadDemo implements Runnable {

    @Override
    public void run() {
        System.out.println("创立线程形式2");
    }

    public static void main(String[] args) {
        ThreadDemo threadDemo = new ThreadDemo();
        //剖析源码
        new Thread(threadDemo).start();
    }

}

3.剖析案例2中的源码得悉
1.Thread实现了Runnable接口,重写了run办法
2.threadDemo在构造函数中作为参数传递给Thread中的target属性
3.当执行线程的run办法时,target(threadDemo)执行子类重写的run办法,实现业务逻辑

public Thread(Runnable target) {
    init(null, target, "Thread-" + nextThreadNum(), 0);
}
//只展现局部代码
private void init(ThreadGroup g, Runnable target, String name,
                  long stackSize, AccessControlContext acc,
                  boolean inheritThreadLocals) {
    if (name == null) {
        throw new NullPointerException("name cannot be null");
    }
    this.name = name;    
    SecurityManager security = System.getSecurityManager();
    this.group = g;  
    this.priority = parent.getPriority();  
    **this.target = target; ** 
}

@Override
public void run() {
    if (target != null) {
        target.run();
    }
}

无论哪种形式创立线程,实质都是实现了Runnable接口,重写了run办法。间接调用run办法不属于多线程

Java线程的创立调用过程如上图所示。首先,Java线程的start办法会创立一个本地线程（通过调用JVM_StartThread），该线程的线程函数是定义在jvm.cpp中的thread_entry，由其再进一步调用run办法。能够看到Java线程的run办法和一般办法其实没有本质区别，间接调用run办法不会报错，然而却是在以后线程执行，而不会创立一个新的线程。

4.FutureTask,Callable，FutureTask也能够创立线程,并且能够取得返回值

FutureTask实现了Runnable接口重写run办法，同时能够作为参数传入Thread的构造函数。实现了Future接口,能够通过get(),cancel()获取返回值,勾销线程。

public class FutureTaskDemo implements Callable<String> {
    
    @Override
    public String call() throws Exception {
        System.out.println("重写Callable中的call办法");
        return "success";
    }

    public static void main(String[] args) throws ExecutionException, InterruptedException, TimeoutException {
        FutureTask task = new FutureTask(new FutureTaskDemo());        
        new Thread(task).start();
        //获取返回值
        System.out.println(task.get());
    }
    
}

通过上面对Thread的剖析大抵, 在Thread中调用FutureTask的实例的run办法,而后run()中调用了Callable实例的call办法,执行业务逻辑。同时获取返回值。

援用文章：https://segmentfault.com/a/11…