关于volatile的可见性和禁止指令重排序的疑惑

package com.aaron.beginner.multithread.volatiletest;

import java.util.concurrent.CountDownLatch;

/**
 * @author 
 * @description 一句话描述该文件的用途
 * @date 2017-03-01
 */
public class VolatileAndNonVolatileTest
{

    private volatile boolean flag;

    private int num;


    public static void main(String[] args) throws InterruptedException
    {

        for (int i = 0; i < 5000; i++)
        {
            final VolatileAndNonVolatileTest test = new VolatileAndNonVolatileTest();

            CountDownLatch latch = new CountDownLatch(2);
            Thread write = new Thread(() ->
            {
                test.write();
                latch.countDown();
            });

            Thread read = new Thread(() ->
            {
                test.read();
                latch.countDown();
            });

            write.start();
            read.start();

            latch.await();
        }
    }


    private void read()
    {
        if (flag)
        {
            System.out.println("=" + num * num);
        }
    }


    private void write()
    {
        num = 10;//步骤1

        flag = true;//步骤2

    }

}