How does Java use IO streams to implement simple notepad functions?

Requirements: Write a program that simulates a diary. By entering commands on the console, you can create new files locally, open the diary, and modify the diary.

Command 1 represents "New Diary", which can obtain the diary content input by the user from the console.

Command 2 represents "Open Diary", which reads the contents of the TXT file with the specified path and Output to the console

Command 3 represents "modify diary", modify the original content in the journal

Command 4 represents save

Command 5 represents exit

import java.io.*;
import java.util.Scanner;
public class IO_日记本 {
    /**
     * 模拟日记本程序
     */
    private static String filePath;
    private static String message = "";
 
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        while (true) {
            System.out.println("---------日记本---------");
            System.out.println("1.写日记");
            System.out.println("2.查看日记");
            System.out.println("3.修改日记");
            System.out.println("4.保存");
            System.out.println("5.退出");
            System.out.println("注意：每次输入内容后记得保存！");
            System.out.print("请输入操作指令：");
            int command = sc.nextInt();
            switch (command) {
                case 1:
                    // 1:新建文件（写日记）
                    createFile();
                    break;
                case 2:
                    // 2:打开文件（查看日记）
                    openFile();
                    break;
                case 3:
                    // 3:修改文件
                    editFile();
                    break;
                case 4:
                    // 4:保存
                    saveFile();
                    break;
                case 5:
                    // 5:退出
                    System.out.println("谢谢使用本系统，欢迎下次再来！");
                    System.exit(0);
                    break;
                default:
                    System.out.println("您输入的指令错误！");
                    break;
            }
        }
    }
 
    //写一个方法写入文件内容
    private static void createFile() {
        message = "";//新建文件时，暂存文件内容清空
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入内容，停止编写请输入：stop");
        StringBuffer stb = new StringBuffer();//用于后期输入内容的拼接
        String inputMessage = "";
        while (!inputMessage.equals("stop")) {//输入stop则停止
            if (stb.length() > 0) {
                stb.append("\r\n");//追加换行符
            }
            stb.append(inputMessage);//拼接输入信息
            inputMessage = sc.nextLine();//获取输入信息
        }
        message = stb.toString();//将输入内容缓存
    }
 
    //写一个方法保存文件
    private static void saveFile() throws Exception {
        FileWriter out = new FileWriter("文件路径", true);
        out.write(message + "\r\n");//将输入内容写入
        message = "";
        out.close();
    }
 
    //写一个方法打开文件
    public static void openFile() throws Exception {
        Reader r = new FileReader("文件路径");
        BufferedReader br = new BufferedReader(r);
//        char[] c = new char[1024];//定义一个桶装每次读取多少个数据
//        int len;
//        while ((len = br.read(c)) != -1) {//读取所有内容，如果读完所有内容则停止
//            String str = new String(c, 0, len);//每次读取0到len的所有内容
//            System.out.print(str);//因为读取时会自动换行所以这里我们不需要换行
//        }
        String line;
        while ((line = br.readLine()) != null) {//一次读取一行
            System.out.println(line);//因为读取一行时程序不会自己换行，所以这里我们需要给它换行
        }
        //System.out.println();//读完换行
    }
 
    //写一个方法修改文件
    /**
     * 替换
     * @throws IOException
     */
    public static void editFile() throws IOException{
        Scanner sc = new Scanner(System.in);
        //原有的内容
        System.out.println("原文件内容：");
        String str1 =sc.next();;
        //要替换的内容
        System.out.println("修改成：");
        String str2 =sc.next();
        // 读取
        File file = new File("文件路径");
        FileReader in = new FileReader(file);
        BufferedReader buf = new BufferedReader(in);//缓冲流
        // 内存流, 作为临时流
        CharArrayWriter tempStream = new CharArrayWriter();
        // 替换
        String line = null;
        while ( (line = buf.readLine()) != null) {
            // 替换每行中, 符合条件的字符串
            line = line.replaceAll(str1, str2);//正则表达式
            // 将该行写入内存
            tempStream.write(line+"\r\n");
        }
        // 关闭输入流
        buf.close();
        // 将内存中的流写入文件
        FileWriter fw = new FileWriter(file);
        tempStream.writeTo(fw);
        fw.close();
    }
}

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