java/w7/Main.java

import java.io.*;
import java.util.ArrayList;
import java.util.List;

// =============== 自定义异常类（面向对象体现） ===============
class InvalidScoreException extends Exception {
    public InvalidScoreException(String message) {
        super(message);
    }
}

// =============== 成绩处理器类 ===============
class ScoreProcessor {
    private List<Integer> scores = new ArrayList<>();

    /**
     * 从指定文件读取成绩
     * @param filename 文件名
     * @throws IOException 文件读取错误
     * @throws InvalidScoreException 成绩格式无效
     */
    public void loadScoresFromFile(String filename) throws IOException, InvalidScoreException {
        scores.clear();
        try (BufferedReader reader = new BufferedReader(new FileReader(filename))) {
            String line;
            int lineNumber = 0;
            while ((line = reader.readLine()) != null) {
                lineNumber++;
                line = line.trim();
                if (line.isEmpty()) continue; // 跳过空行

                try {
                    int score = Integer.parseInt(line);
                    if (score < 0 || score > 100) {
                        throw new InvalidScoreException("第 " + lineNumber + " 行：成绩应在 0~100 之间，但得到 " + score);
                    }
                    scores.add(score);
                } catch (NumberFormatException e) {
                    throw new InvalidScoreException("第 " + lineNumber + " 行：\"" + line + "\" 不是有效的整数");
                }
            }
        }
    }

    /**
     * 计算平均分
     * @return 平均分（保留两位小数）
     * @throws IllegalStateException 如果没有有效成绩
     */
    public double calculateAverage() {
        if (scores.isEmpty()) {
            throw new IllegalStateException("没有可计算的有效成绩");
        }
        int sum = scores.stream().mapToInt(Integer::intValue).sum();
        return Math.round((double) sum / scores.size() * 100) / 100.0;
    }

    public int getScoreCount() {
        return scores.size();
    }
}

// =============== 主类 ===============
public class Main {
    public static void main(String[] args) {
        ScoreProcessor processor = new ScoreProcessor();

        try {
            processor.loadScoresFromFile("scores.txt");
            double average = processor.calculateAverage();
            System.out.printf("共读取 %d 条有效成绩，平均分：%.2f%n",
                    processor.getScoreCount(), average);
        } catch (FileNotFoundException e) {
            System.err.println("❌ 文件未找到：请确保 'scores.txt' 存在于当前目录。");
        } catch (IOException e) {
            System.err.println("❌ 读取文件时发生 I/O 错误：" + e.getMessage());
        } catch (InvalidScoreException e) {
            System.err.println("❌ 成绩数据格式错误：" + e.getMessage());
        } catch (IllegalStateException e) {
            System.err.println("❌ 数据不足：" + e.getMessage());
        }
    }
}