/**
 * The <code>Runnable</code> interface should be implemented by any
 * class whose instances are intended to be executed by a thread. The
 * class must define a method of no arguments called <code>run</code>.
 * <p>
 * This interface is designed to provide a common protocol for objects that
 * wish to execute code while they are active. For example,
 * <code>Runnable</code> is implemented by class <code>Thread</code>.
 * Being active simply means that a thread has been started and has not
 * yet been stopped.
 * <p>
 * In addition, <code>Runnable</code> provides the means for a class to be
 * active while not subclassing <code>Thread</code>. A class that implements
 * <code>Runnable</code> can run without subclassing <code>Thread</code>
 * by instantiating a <code>Thread</code> instance and passing itself in
 * as the target.  In most cases, the <code>Runnable</code> interface should
 * be used if you are only planning to override the <code>run()</code>
 * method and no other <code>Thread</code> methods.
 * This is important because classes should not be subclassed
 * unless the programmer intends on modifying or enhancing the fundamental
 * behavior of the class.
 *
 * @author  Arthur van Hoff
 * @see     java.lang.Thread
 * @see     java.util.concurrent.Callable
 * @since   JDK1.0
 */
@FunctionalInterface
public interface Runnable {
    /**
     * When an object implementing interface <code>Runnable</code> is used
     * to create a thread, starting the thread causes the object's
     * <code>run</code> method to be called in that separately executing
     * thread.
     * <p>
     * The general contract of the method <code>run</code> is that it may
     * take any action whatsoever.
     *
     * @see     java.lang.Thread#run()
     */
    public abstract void run();
}

The <code>Runnable</code> interface should be implemented by any
 * class whose instances are intended to be executed by a thread. The
 * class must define a method of no arguments called <code>run</code>.

译文：Runnable接口应该由旨在由线程执行的任何类实例实现。 该类必须定义一个没有参数的run方法。

 This interface is designed to provide a common protocol for objects that
 * wish to execute code while they are active. For example,
 * <code>Runnable</code> is implemented by class <code>Thread</code>.
 * Being active simply means that a thread has been started and has not
 * yet been stopped

译文：此接口旨在为希望在活动状态下执行代码的对象提供通用协议。 例如，Runnable由Thread类实现。处于活动状态仅表示一个线程已经启动但尚未停止

 In addition, <code>Runnable</code> provides the means for a class to be
 * active while not subclassing <code>Thread</code>. A class that implements
 * <code>Runnable</code> can run without subclassing <code>Thread</code>
 * by instantiating a <code>Thread</code> instance and passing itself in
 * as the target.  In most cases, the <code>Runnable</code> interface should
 * be used if you are only planning to override the <code>run()</code>
 * method and no other <code>Thread</code> methods.
 * This is important because classes should not be subclassed
 * unless the programmer intends on modifying or enhancing the fundamental
 * behavior of the class.

译文：另外，Runnable提供了一种在不继承Thread的情况下使类处于活动状态的方法。 实现Runnable的类可以通过实例化Thread实例并将其自身作为目标传递而无需继承Thread的子类。 在大多数情况下，如果您仅打算覆盖run（）方法而没有其他Thread方法，则应使用Runnable接口。 这很重要，因为除非程序员打算修改或增强类的基本行为，否则不应将类归为子类。

Runnable着重点在于运行在线程中。

对于线程的实现，官方提供了两种方法，第一种是继承Thread类，重写Run方法；第二种是实现Runnable接口。上面源码推荐使用实现Runnable接口来创建线程