解析java中volatile关键字

public class ThreadSee { 
//t1线程会根据flag的值做对应的操作，主线程会更改t1的值 
 public static void main(String[] args) throws InterruptedException { 
    ThReadTest th= new ThReadTest(); 
    Thread t1 = new Thread(th); 
    t1.start(); 
    Thread.sleep(1000); 
    th.changeFlag(); 
    Thread.sleep(2000); 
    System.out.println(th.getFlag()); 
  } 
 
} 
 
 
class ThReadTest implements Runnable{ 
 
  //线程访问变量时会把其load到对应的线程栈中，每次操作时都要获取内存中最新的数据 
  private volatile boolean stopflag; 
  @Override 
  public void run() { 
    int i=0; 
    while(!stopflag){ 
      i++; 
      System.out.println("=="+Thread.currentThread().getName()); 
    } 
    System.out.println("Thread finish:"+i); 
  } 
  public void changeFlag(){ 
    this.stopflag=true; 
    System.out.println(Thread.currentThread().getName()+"***********"); 
  } 
 
  public boolean getFlag(){ 
    return stopflag; 
  } 
} 

public class ThreadSave implements Runnable{ 
  static ThreadSave sync = new ThreadSave(); 
  static volatile int j=0; 
  //Lock lock =new ReentrantLock(); 
  public void inscane(){ 
    // lock.lock(); 
    for(int i=0;i<10000000;i++){ 
      j++; 
    } 
   //  lock.unlock(); 
  } 
  @Override 
  public void run() { 
    inscane(); 
  } 
  public static void main(String[] args) throws InterruptedException { 
    Thread t1 = new Thread(sync); 
    Thread t2 = new Thread(sync); 
    t1.start(); 
    t2.start(); 
    t1.join(); 
    t2.join(); 
    System.out.println(j); 
  } 
}