Java 制作四则运算题库

前几天，母上找我给我小妹（一年级生）做个四则运算题库程序。
我顶着被我妹骂的压力，紧赶慢赶做了出来。
用到了这几天学的Swing组件。
比较繁琐，以后可能会改进。

运算类

import com.sun.xml.internal.bind.WhiteSpaceProcessor;

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Random;

public class Operation extends JFrame implements ActionListener {
   
   
    //定义加减乘除的数字
    int Add_a,Add_b,Add_c;
    int Sub_a,Sub_b,Sub_c;
    int Mul_a,Mul_b,Mul_c;
    int Div_a,Div_b = 1,Div_c,Div_mod;


    //上一题下一题的按钮
    private JButton NextTest;
    private JButton EndStudy;

    //定义一个提交按钮
    private JButton Submit;

    //定义运算式的文本
    private JLabel Explain;
    private JLabel Explain_MOD;

    //定义一个文本框用来判断输入的数字是否正确
    private JTextField
            StudyTestADD = new JTextField(20),
            StudyTestSUB = new JTextField(20),
            StudyTestMUL = new JTextField(20),
            StudyTestDIV = new JTextField(20);
    private JTextField
            Answer = new JTextField(3),
            Answer_MOD = new JTextField(3);
    private JTextField Result = new JTextField(50);
    //随机数
    Random random = new Random();
    //定义的这个是为了随机加减乘除
    int Operation_random = random.nextInt(4);

    public void CreateTestWindow(){
   
   
        Explain = new JLabel("你的答案是:");
        this.add(Explain);
        Explain.setBounds(150,100,150,50);
        Explain.setFont(new Font("宋体", Font.BOLD,20));

        Explain_MOD = new JLabel("如果是除法,那么它的余数是:");
        this.add(Explain_MOD);
        Explain_MOD.setBounds(50,160,450,50);
        Explain_MOD.setFont(new Font("宋体", Font.BOLD,20));

        this.add(Answer);
        Answer.setBounds(300,100,50,50);
        Answer.setFont(new Font("宋体", Font.BOLD,20));

        this.add(Answer_MOD);
        Answer_MOD.setBounds(460,160,50,50);
        Answer_MOD.setFont(new Font("宋体", Font.BOLD,20));

        Submit = new JButton("提交");