java中volatile不能保证线程安全(实例讲解)

/** *  * 类简要描述 *  * <p> * 类详细描述 * </p> *  * @author think *  */public class VolatileThread implements Runnable { private volatile int a = 0; @Override public void run() {  // TODO Auto-generated method stub//  synchronized (this) {   a = a + 1;   System.out.println(Thread.currentThread().getName() + ":----" + a);   try {    Thread.sleep(100);    a = a + 2;   } catch (InterruptedException e) {    // TODO Auto-generated catch block    e.printStackTrace();   }   System.out.println(Thread.currentThread().getName() + ":----" + a);//  } }}

/** *  * 类简要描述 *  * <p> * 类详细描述 * </p> *  * @author think *  */public class VolatileMain { public static void main(String[] args) {  VolatileThread s = new VolatileThread();  Thread t1 = new Thread(s);  Thread t2 = new Thread(s);  Thread t3 = new Thread(s);  Thread t4 = new Thread(s);  t1.start();  t2.start();  t3.start();  t4.start();    /*  同步的结果  Thread-2:----1  Thread-2:----3  Thread-0:----4  Thread-0:----6  Thread-3:----7  Thread-3:----9  Thread-1:----10  Thread-1:----12*/  /*    去掉同步的结果  Thread-0:----1  Thread-1:----2  Thread-2:----3  Thread-3:----4  Thread-0:----8  Thread-3:----10  Thread-1:----10  Thread-2:----12*/   }}