用java编写一个不同年级自主学习的四则运算练习的程序，要求完成如下功能： （1） 用随机函数生成10个随机的四则运算，限制在两位数以内，超过的则用异常提醒 （2） 对于减法和除法要判断结果不能出现负数和除数不能为零，同时处理异常。 （3） 用户输入每一个的运算结果，然后并判断对错，对则加一分，最终计算出最终得分。 （4） 菜单能够循环让用户选择是否继续，直到选择结束而关闭程序。 （5） 判断对错需要一个单独的类，计分需要一个单独的类 （6） 一年级的学生，只有加减；三年级学生有加减乘除。构建父类和子类关系

以下是一个简单的实现，包含了一个父类和两个子类，分别为一年级和三年级的学生。其中，父类为题目生成器类，子类为题目校验类和计分类。

题目生成器类：

import java.util.Random;

public class QuestionGenerator {
    private Random random = new Random();

    public String generateQuestion() throws Exception {
        int num1 = random.nextInt(100);
        int num2 = random.nextInt(100);
        int operator = random.nextInt(4);
        String op;
        int result;

        switch (operator) {
            case 0:
                op = "+";
                result = num1 + num2;
                break;
            case 1:
                op = "-";
                if (num1 < num2) {
                    throw new Exception("Subtraction may produce negative result");
                }
                result = num1 - num2;
                break;
            case 2:
                op = "*";
                result = num1 * num2;
                break;
            case 3:
                op = "/";
                if (num2 == 0) {
                    throw new Exception("Division by zero");
                }
                if (num1 % num2 != 0) {
                    throw new Exception("Division may produce non-integer result");
                }
                result = num1 / num2;
                break;
            default:
                throw new Exception("Invalid operator");
        }

        return String.format("%d %s %d = ", num1, op, num2);
    }
}

题目校验类：

public class AnswerValidator {
    public static boolean isValid(int answer, String question) throws Exception {
        String[] parts = question.split(" ");
        int num1 = Integer.parseInt(parts[0]);
        String op = parts[1];
        int num2 = Integer.parseInt(parts[2]);
        int expected;

        switch (op) {
            case "+":
                expected = num1 + num2;
                break;
            case "-":
                expected = num1 - num2;
                break;
            case "*":
                expected = num1 * num2;
                break;
            case "/":
                if (num2 == 0) {
                    throw new Exception("Division by zero");
                }
                if (num1 % num2 != 0) {
                    throw new Exception("Division may produce non-integer result");
                }
                expected = num1 / num2;
                break;
            default:
                throw new Exception("Invalid operator");
        }

        return answer == expected;
    }
}

计分类：

public class ScoreCounter {
    private int score = 0;

    public void addScore() {
        score++;
    }

    public int getScore() {
        return score;
    }
}

主程序：

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        QuestionGenerator generator = new QuestionGenerator();
        ScoreCounter counter = new ScoreCounter();
        boolean keepGoing = true;

        while (keepGoing) {
            System.out.print("Please enter the grade level (1 or 3): ");
            int grade = scanner.nextInt();
            scanner.nextLine();

            int numQuestions = 10;
            if (grade == 1) {
                System.out.println("Generating 10 addition/subtraction questions for first grade...");
            } else if (grade == 3) {
                System.out.println("Generating 10 addition/subtraction/multiplication/division questions for third grade...");
            } else {
                System.out.println("Invalid grade level");
                continue;
            }

            for (int i = 1; i <= numQuestions; i++) {
                String question;
                try {
                    question = generator.generateQuestion();
                } catch (Exception e) {
                    System.out.println(e.getMessage());
                    i--;
                    continue;
                }
                System.out.print(question);
                int answer = scanner.nextInt();
                scanner.nextLine();

                boolean validAnswer;
                try {
                    validAnswer = AnswerValidator.isValid(answer, question);
                } catch (Exception e) {
                    System.out.println(e.getMessage());
                    i--;
                    continue;
                }

                if (validAnswer) {
                    System.out.println("Correct!");
                    counter.addScore();
                } else {
                    System.out.println("Wrong!");
                }
            }

            System.out.printf("Your score is %d out of %d\n", counter.getScore(), numQuestions);
            System.out.print("Do you want to continue (y/n)? ");
            String answer = scanner.nextLine();
            keepGoing = answer.equalsIgnoreCase("y");
        }
    }
}