静态同步synchronized方法和synchronized(class)代码块

关键字synchronized还可以应用在static静态方法上，如果这样写，那是对当前的*.java文件对应的Class类进行持锁。

package synStaticMethod;

/**
 * Created by Administrator on 2017/1/22 0022.
 */
public class Service {
    synchronized public  static  void printA(){
        try{
        System.out.println("线程名称为："+Thread.currentThread().getName()+"在"+System.currentTimeMillis()+"进入printA");
            Thread.sleep(3000);
            System.out.println("线程名称为："+Thread.currentThread().getName()+"在"+System.currentTimeMillis()+"离开printA");

        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    synchronized public static  void printB(){
        System.out.println("线程名称为："+Thread.currentThread().getName()+"在"+System.currentTimeMillis()+"进入printB");
        System.out.println("线程名称为："+Thread.currentThread().getName()+"在"+System.currentTimeMillis()+"离开printB");

    }
}

package synStaticMethod;


/**
 * Created by Administrator on 2017/1/22 0022.
 */
public class ThreadA extends Thread{
    public void run(){
        Service.printA();
    }
}

package synStaticMethod;

/**
 * Created by Administrator on 2017/1/22 0022.
 */
public class ThreadB extends Thread {
    public void run(){
        Service.printB();
    }
}

package synStaticMethod;

/**
 * Created by Administrator on 2017/1/22 0022.
 */
public class Run {
    public static  void main(String[]args){
        ThreadA threadA =  new ThreadA();
        threadA.setName("A");
        threadA.start();
        ThreadB threadB = new ThreadB();
        threadB.setName("B");
        threadB.start();
    }
}

线程名称为：A在1485063366543进入printA
线程名称为：A在1485063369543离开printA
线程名称为：B在1485063369543进入printB
线程名称为：B在1485063369543离开printB

从结果来看，是同步的效果，和将synchronized关键字加到非静态方法上使用的效果是一样的，其实synchronized关键字加到static静态方法上是给Class类上锁，而synchronized关键字加到非static静态方法上是给对象加锁。