用Java语言编写代码，要求批量产生并存储习题（CSV文件格式），加、减、混合题各一套；加一个类ExerciseFiles、在其中增加方法，从CSV格式的文件中读入习题。屏幕显示读到的文件内容。在上述基础上添加运算结果，例如33+22=55，屏幕显示，要求复用算式类；

好的，让我为您提供一份Java代码样例，实现您的需求：

BinaryOperation.java

public class BinaryOperation {
    private int operand1;
    private int operand2;
    private char operator;

    public BinaryOperation(int operand1, int operand2, char operator) {
        this.operand1 = operand1;
        this.operand2 = operand2;
        this.operator = operator;
    }

    public int calculate() {
        switch (operator) {
            case '+':
                return operand1 + operand2;
            case '-':
                return operand1 - operand2;
            default:
                throw new IllegalArgumentException("Unsupported operator: " + operator);
        }
    }

    @Override
    public String toString() {
        return operand1 + " " + operator + " " + operand2;
    }
}

Exercise.java

import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;

public class Exercise {
    private List<BinaryOperation> operations;

    public Exercise(int numAdd, int numSubtract, int numMixed) {
        operations = new ArrayList<BinaryOperation>();
        Random rand = new Random();
        for (int i = 0; i < numAdd; i++) {
            int a = rand.nextInt(100);
            int b = rand.nextInt(100);
            operations.add(new BinaryOperation(a, b, '+'));
        }
        for (int i = 0; i < numSubtract; i++) {
            int a = rand.nextInt(100);
            int b = rand.nextInt(100);
            operations.add(new BinaryOperation(a, b, '-'));
        }
        for (int i = 0; i < numMixed; i++) {
            int a = rand.nextInt(100);
            int b = rand.nextInt(100);
            char operator = rand.nextBoolean() ? '+' : '-';
            operations.add(new BinaryOperation(a, b, operator));
        }
    }

    public void saveToFile(String filename) {
        try (FileWriter writer = new FileWriter(filename)) {
            for (BinaryOperation op : operations) {
                writer.write(op.toString() + "\n");
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public List<BinaryOperation> getOperations() {
        return operations;
    }
}

ExerciseSheet.java

import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

public class ExerciseSheet {
    private List<Exercise> exercises;

    public ExerciseSheet(int numAdd, int numSubtract, int numMixed, int numSheets) {
        exercises = new ArrayList<Exercise>();
        for (int i = 0; i < numSheets; i++) {
            exercises.add(new Exercise(numAdd, numSubtract, numMixed));
        }
    }

    public void saveToFile(String prefix) {
        for (int i = 0; i < exercises.size(); i++) {
            String filename = prefix + "-" + (i + 1) + ".csv";
            exercises.get(i).saveToFile(filename);
        }
    }

    public List<Exercise> getExercises() {
        return exercises;
    }
}

ExerciseFiles.java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

public class ExerciseFiles {
    public static List<BinaryOperation> readFromFile(String filename) {
        List<BinaryOperation> operations = new ArrayList<BinaryOperation>();
        try (BufferedReader reader = new BufferedReader(new FileReader(filename))) {
            String line;
            while ((line = reader.readLine()) != null) {
                String[] parts = line.split("\\s+");
                int a = Integer.parseInt(parts[0]);
                char operator = parts[1].charAt(0);
                int b = Integer.parseInt(parts[2]);
                operations.add(new BinaryOperation(a, b, operator));
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return operations;
    }

    public static void printOperations(List<BinaryOperation> operations) {
        for (BinaryOperation op : operations) {
            int result = op.calculate();
            System.out.println(op.toString() + " = " + result);
        }
    }
}

这份代码样例中，BinaryOperation类表示二元操作，Exercise类表示一组二元操作，ExerciseSheet类表示多组二元操作，ExerciseFiles类表示从文件中读取和显示二元操作。

您可以将这份代码保存为ExerciseDemo.java文件，并执行以下代码：

public class ExerciseDemo {
    public static void main(String[] args) {
        ExerciseSheet sheet = new ExerciseSheet(10, 10, 10, 3);
        sheet.saveToFile("exercises");
        List<BinaryOperation> operations = ExerciseFiles.readFromFile("exercises-1.csv");
        ExerciseFiles.printOperations(operations);
    }
}

这份代码会生成三组加、减、混合题各十道的习题，保存在exercises-1.csv、exercises-2.csv、exercises-3.csv三个文件中，并从exercises-1.csv文件中读取二元操作，并计算并显示结果。