synchronized关键字实现线程安全

/**
 * Created by it on 2017/6/7.
 */
public class MyThread extends Thread {
    private  int val;
    private Service service;
    static RealExecu realExecu=new RealExecu();
    public MyThread(int v) {
        val = v;
    }
    public MyThread(Service service) {
        this.service = service;
    }
    //这种做法是非线程安全的
    public synchronized void print1(int v) throws InterruptedException {
        for (int i = 0; i < 100; i++) {
            Thread.sleep(100);
            System.out.print(v);
        }
    }

    public void print2(int v) throws InterruptedException {
        //线程安全
        synchronized (MyThread.class) {
            for (int i = 0; i < 100; i++) {
                Thread.sleep(100);
                System.out.print(v);
            }
        }
    }

    public void run() {

    try {
            realExecu.print(val);
        }
      
        //print1(val);}
             //print2(val);}

   catch (InterruptedException ie){

        }
    }
}

/**
 * Created by it on 2017/6/7.
 */
public class ThreadTest {
    public static void main(String[] args) {
        MyThread m1 = new MyThread(1);
        MyThread m2 = new MyThread(2);
      
        m1.start();
        m2.start();
    }
}
print1方法上加上synchronized，没有起同步作用，是因为该方法被不同实例调用，实现同步可以使用print2方法，在类实例上加锁；
print2方法等同于把方法放入一个类中，在mythread中定义静态类实例变量，以实现synchronized的同步作用

public class RealExecu {
    public synchronized  void print(int v) throws InterruptedException {
        for (int i = 0; i < 100; i++) {
            Thread.sleep(100);
            System.out.print(v);
        }
    }
}