2）从文件中读取各学生成绩，计算所有学生成绩的平均值，将成绩的最大值、最小值及平均值并存入文本文件中。 （3）将上面两个文本文件的内容合并到一个新的文本文件中。 2．统计一个文本文件中字母'A'和'a'出现的总次数。

第一题：

1. 从文件中读取各学生成绩：

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class Main {
    public static void main(String[] args) {
        try {
            FileReader reader = new FileReader("data.txt");
            BufferedReader bufferedReader = new BufferedReader(reader);

            String line;
            double sum = 0;
            int count = 0;
            double max = Double.MIN_VALUE;
            double min = Double.MAX_VALUE;

            while ((line = bufferedReader.readLine()) != null) {
                String[] parts = line.split(" ");
                double score = Double.parseDouble(parts[2]);
                sum += score;
                count++;
                if (score > max) {
                    max = score;
                }
                if (score < min) {
                    min = score;
                }
            }

            double average = sum / count;

            // 将成绩的最大值、最小值及平均值存入文本文件
            FileWriter writer = new FileWriter("result.txt");
            writer.write("最大值：" + max + "\n");
            writer.write("最小值：" + min + "\n");
            writer.write("平均值：" + average + "\n");
            writer.close();

            bufferedReader.close();
            reader.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

2. 将上面两个文本文件的内容合并到一个新的文本文件中：

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class Main {
    public static void main(String[] args) {
        try {
            // 读取成绩文件
            FileReader reader1 = new FileReader("data.txt");
            BufferedReader bufferedReader1 = new BufferedReader(reader1);

            String line;
            double sum = 0;
            int count = 0;
            double max = Double.MIN_VALUE;
            double min = Double.MAX_VALUE;

            while ((line = bufferedReader1.readLine()) != null) {
                String[] parts = line.split(" ");
                double score = Double.parseDouble(parts[2]);
                sum += score;
                count++;
                if (score > max) {
                    max = score;
                }
                if (score < min) {
                    min = score;
                }
            }

            double average = sum / count;

            bufferedReader1.close();
            reader1.close();

            // 将成绩的最大值、最小值及平均值存入文本文件
            FileWriter writer1 = new FileWriter("result.txt");
            writer1.write("最大值：" + max + "\n");
            writer1.write("最小值：" + min + "\n");
            writer1.write("平均值：" + average + "\n");
            writer1.close();

            // 读取字母统计文件
            FileReader reader2 = new FileReader("letter_count.txt");
            BufferedReader bufferedReader2 = new BufferedReader(reader2);

            // 将两个文件的内容合并到一个新文件中
            FileWriter writer2 = new FileWriter("merged.txt");
            while ((line = bufferedReader2.readLine()) != null) {
                writer2.write(line + "\n");
            }
            writer2.write("\n");
            writer2.write("成绩统计结果：\n");
            writer2.write("最大值：" + max + "\n");
            writer2.write("最小值：" + min + "\n");
            writer2.write("平均值：" + average + "\n");
            writer2.close();

            bufferedReader2.close();
            reader2.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

第二题：统计一个文本文件中字母'A'和'a'出现的总次数

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class Main {
    public static void main(String[] args) {
        try {
            FileReader reader = new FileReader("text.txt");
            BufferedReader bufferedReader = new BufferedReader(reader);

            int countA = 0;
            int counta = 0;

            String line;
            while ((line = bufferedReader.readLine()) != null) {
                for (char c : line.toCharArray()) {
                    if (c == 'A') {
                        countA++;
                    }
                    if (c == 'a') {
                        counta++;
                    }
                }
            }

            FileWriter writer = new FileWriter("letter_count.txt");
            writer.write("A出现次数：" + countA + "\n");
            writer.write("a出现次数：" + counta + "\n");
            writer.close();

            bufferedReader.close();
            reader.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}