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JAVA实验7 输入输出流I/O

脱下愤怒的小裤衩 2022-05-05 阅读 65
java

实验7 输入输出流I/O

实验要求:
(1)掌握File类;
(2)掌握常用字节流类;
(3)掌握常用的字符流及缓冲流的使用。
实验内容:
(1)按行读取文件studentInfo.txt的内容,获取学生姓名并写入到studentName.txt文件中,且给每一行按序加上行号;获取studentName.txt文件的长度及修改时间。
studentInfo.txt文件内容格式如下:
王珊珊,王珊珊,20132213806,2015-10-10 14:30:56
张国辉,张国辉,20132213944,2015-10-10 14:31:05
蒋宇宙,蒋宇宙,20132213906,2015-10-10 14:31:24
王燕萍,王燕萍,20132213847,2015-10-10 14:31:16

import java.io.*;
import java.text.SimpleDateFormat;

public class StudentIO1 {
    private static final String fr ="test7/src/studentInfo.txt";
    private static final String fw ="test7/src/studentName.txt";

    public static void main(String[] args) {
        try (BufferedReader br = new BufferedReader(new FileReader(fr));
             BufferedWriter bw = new BufferedWriter(new FileWriter(fw));
             ){
            String line;
            Integer cnt = 1;
            while ((line = br.readLine()) != null){
                String[] arr = line.split(","); //根据逗号分割
                bw.write(  cnt.toString()+"、"+arr[0]);
                bw.newLine();
                cnt++;
//                System.out.println(line);
            }
            File f = new File(fw);
            System.out.println("studentName.txt文件的长度:"+f.length());
            SimpleDateFormat time = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
            System.out.println("studentName.txt文件的修改时间:"+time.format(f.lastModified()));

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

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(2)学生成绩存储在文件中,每行一个学生成绩,形如:
20151201 85 84 91.5
20151202 70 85 65

请编程读入学生成绩,并计算各门课程的均值和方差,写入文件的最后一行,如:
均值和方差 71/10 81.2/11.3 76/15.3

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

public class StudentGradeIO {
    private static final String f ="test7/src/studentGrade.txt";

    public static void main(String[] args) {

        try(BufferedReader br1 = new BufferedReader(new FileReader(f));
            BufferedReader br2 = new BufferedReader(new FileReader(f));
            BufferedWriter bw = new BufferedWriter(new FileWriter(f, true))
        ) {
            String line;
            int n = 0;  //总人数
            String[] arr = null;
            ArrayList<Double> sc = new ArrayList<>(100);   //存放每一科成绩的平均分
             ArrayList<Double> var = new ArrayList<>(100);   //存放每一科成绩的方差
            for (int i = 0; i < 100; i++){  //初始化
                sc.add(0.0);
                var.add(0.0);
            }

            while ((line = br1.readLine()) != null)
            {
                arr = line.replaceAll(" +", " ").split(" "); //根据空格分割
                for (int i = 1; i < arr.length; i++) {
                    sc.set(i, sc.get(i) + Double.parseDouble(arr[i]));
//                    System.out.print(sc.get(i)); System.out.print("  ");
                }
                n++;
            }
            for (int i = 1; i < arr.length; i++)    //求每科的平均分
                sc.set(i, sc.get(i) / n);

            //求方差
            while ((line = br2.readLine()) != null)
            {
                 arr = line.replaceAll(" +", " ").split(" "); //根据空格分割
                 for (int i = 1; i < arr.length; i++) {
                     var.set(i, var.get(i) + (Double.parseDouble(arr[i]) - sc.get(i)) * (Double.parseDouble(arr[i]) - sc.get(i)));
                 }
            }
            bw.newLine();
            bw.write("均值和方差");
            for (int i = 1; i < arr.length; i++)    //求每科的方差---并写入文件
            {
                var.set(i, var.get(i) / n);
                bw.write("\t"+String.valueOf(sc.get(i))+"/"+String.valueOf(var.get(i)));
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

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