可以看start()方法的注释部分：
/** * Causes this thread to begin execution; the Java Virtual Machine * calls the <code>run</code> method of this thread. * <p> * The result is that two threads are running concurrently: the * current thread (which returns from the call to the * <code>start</code> method) and the other thread (which executes its * <code>run</code> method). * <p> * It is never legal to start a thread more than once. * In particular, a thread may not be restarted once it has completed * execution. * * @exception IllegalThreadStateException if the thread was already * started. * @see #run() * @see #stop() */也就是说当该线程开始执行的时候，Java虚拟机会自动调用该线程的run()方法。