使用java编写小学三年级竖式计算

import java.util.ArrayList;
 
public class demo {
    public static void main(String[] args) {
        ArrayList<String> num1 = new ArrayList<>();
        ArrayList<String> num2 = new ArrayList<>();
        String str1 = null;
        String str2 = null;
        for (int i = 0; i < 500; i++) {
            //int k=(int)(Math.random()*9)+1;
            int j = (int) (Math.random() * 900) + 100;
            int m = (int) (Math.random() * 9) + 1;
            str1 = (i + 1) + ":" + j + "X" + m;
            int temp = j * m;
            str2 = (i + 1) + ":   " + temp;
            num1.add(str1);
            num2.add(str2);
        }
        for (String s : num1) {
            System.out.print(s + " ");
        }
        for (String s : num2) {
            System.out.print(s + " ");
        }
    }
}