如何正确的在java中使用同步锁

package cn.myThread;public class MyThread implements Runnable { private static int total = 10; @Override public void run() {  synchronized (this){ //使用this对象锁  //synchronized (MyThread.class){ //使用MyThread.class类锁  //synchronized (""){//使用字符串锁   System.out.println(Thread.currentThread().getName() + "正在运行");   try {    Thread.sleep(100);   } catch (InterruptedException e) {    e.printStackTrace();   }   total--;   System.out.println(total);   System.out.println(Thread.currentThread().getName() + "线程结束");  } }} package cn.test;import cn.myThread.MyThread;public class TestMyThread { public static void main(String[] args){  MyThread myThread = new MyThread();  Thread thread = null;  for (int i = 1 ; i <= 5 ; i++){   thread = new Thread(myThread,"线程"+i); //开启5个线程，传入同一个对象   thread.start();  } }} 线程1正在运行9线程1线程结束线程3正在运行8线程3线程结束线程5正在运行7线程5线程结束线程2正在运行6线程2线程结束线程4正在运行5线程4线程结束