IDEA 或者 JDK 会自动优化由于变量共享产生的非线程安全问题吗？

刚接触多线程编程，想复现一下书上写的“实例变量共享导致的非线程安全问题”，但是发现怎么尝试都无法得出错误的结果，运行了几十次都是 5000 ，是因为在某一项生成过程中被自动优化了吗？附上代码：

public class MyThread extends Thread{
    public int getCount() {
        return count;
    }

    private int count = 0;

    @Override
    public void run() {
        super.run();
        for(int i = 0 ; i < 1000 ; i++)
        {
            count++;
        }
    }
}
import static java.lang.Thread.sleep;

public class Main {
    public static void main(String[] args) throws InterruptedException {
        MyThread mythread = new MyThread();

        Thread a = new Thread(mythread,"A");
        Thread b = new Thread(mythread,"B");
        Thread c = new Thread(mythread,"C");
        Thread d = new Thread(mythread,"D");
        Thread e = new Thread(mythread,"E");
        a.start();
        b.start();
        c.start();
        d.start();
        e.start();
        sleep(1000);
        System.out.println(mythread.getCount());
    }
}