为什么随机数产生之后就不变化,再次编译没修改源码也不会改变,可是在源码上做任意改动再编译随机数又会改变,求大神告知是什么问题??

import java.util.Scanner;

class T
{
    public static void main(String[] args){
        int number1 = (int)(System.currentTimeMillis() % 10);
        int number2 = (int)(System.currentTimeMillis() * 7 % 10);
        Scanner input = new Scanner(System.in);
        System.out.print("what is " + number1 + " + " + number2 + " ?");
        int answer = input.nextInt();
        System.out.println(number1 + " + " + number2 + " = " + answer + " is " + (number1 + number2 == answer));

    }
}
这是源码