Thread中的run()

    　　/* What will be run. */
    　　private Runnable target;
       如果线程在创建时传入了Runnable运行对象，那么该对象的run方法将被调用
 1     /**
     * If this thread was constructed using a separate
     * <code>Runnable</code> run object, then that
     * <code>Runnable</code> object's <code>run</code> method is called;
       否则，不做任何事且返回
     * otherwise, this method does nothing and returns.
     * <p>
　　　　Thread的子类应该重写这个方法 
     * Subclasses of <code>Thread</code> should override this method.
     *
     * @see     #start()
     * @see     #stop()
     * @see     #Thread(ThreadGroup, Runnable, String)
     */
    @Override
    public void run() {
        if (target != null) {
            target.run();
        }
    }