Java线程-volatile不能保证原子性

package com.Sychronized;

public class VolatileDemo {

    private volatile int number=0;
    public int getNumber()
    {
        return this.number;
    }
    public void increase()
    {
        this.number++;
    }
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        final VolatileDemo volDemo=new VolatileDemo();
        for(int i=0;i<100;i++)
        {
            new Thread(new Runnable() {
                @Override
                public void run() {
                    volDemo.increase();
                }
            }).start();
        }
        
        //如果还有子线程在运行，主线程就让出CPU资源
        //直到所有的子线程都运行完了，主线程再继续往下执行
        while(Thread.activeCount()>1)
        {
            Thread.yield();
        }
        
        System.out.println("number:"+volDemo.getNumber());
    }

}