以上代码中的"加法习题.txt"文件中只有算式没有答案，但是存在一下代码static List<String> readQuestionsFromFile(String filename) { List<String> questions = new ArrayList<>(); try (Scanner scanner = new Scanner(new File(filename))) { while (scanner.hasNextLine()) { String line = scanner.nextLine(); questions.add(line); } } catch (FileNotFoundException e) { System.out.println("File not found: " + filename); } return questions; } static int evaluateQuestion(String question) { String[] parts = question.split(" "); int a = Integer.parseInt(parts[0]); int b = Integer.parseInt(parts[2]); String operator = parts[1]; if (operator.equals("+")) { return a + b; } else { return a - b; } }，怎样通过以上代码在if (index == 2) {}实现对于文件"答案.txt"的批改

在 if (index == 2) {} 中，可以调用 readQuestionsFromFile(String filename) 方法读取"加法习题.txt"文件中的算式列表，然后遍历每个算式，依次调用 evaluateQuestion(String question) 方法计算出答案，并将计算结果与"答案.txt"文件中的答案进行比较。如果计算结果与答案文件中的答案一致，则算式正确，否则算式错误。可以使用一个计数器来记录正确的算式数量，最终输出正确率。具体代码实现如下：

static void checkAnswers(String questionsFile, String answersFile) {
    List<String> questions = readQuestionsFromFile(questionsFile);
    int total = questions.size();
    int correct = 0;
    try (Scanner scanner = new Scanner(new File(answersFile))) {
        int i = 0;
        while (scanner.hasNextLine() && i < total) {
            String answer = scanner.nextLine();
            String question = questions.get(i);
            int result = evaluateQuestion(question);
            if (result == Integer.parseInt(answer)) {
                correct++;
            }
            i++;
        }
    } catch (FileNotFoundException e) {
        System.out.println("File not found: " + answersFile);
        return;
    }
    double accuracy = (double) correct / total * 100;
    System.out.printf("Accuracy: %.2f%% (%d/%d)\n", accuracy, correct, total);
}

调用方式如下：

checkAnswers("加法习题.txt", "答案.txt");