用Java实现简易记事本

好的，这是一个简单的Java记事本的实现示例：

import java.io.*;
import java.util.Scanner;

public class SimpleNotepad {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.println("Welcome to Simple Notepad!");

        while (true) {
            System.out.println("Enter '1' to create a new file, '2' to open an existing file, or '3' to exit:");
            int choice = scanner.nextInt();

            switch (choice) {
                case 1:
                    createFile();
                    break;
                case 2:
                    openFile();
                    break;
                case 3:
                    System.out.println("Exiting Simple Notepad...");
                    System.exit(0);
                    break;
                default:
                    System.out.println("Invalid choice. Please try again.");
            }
        }
    }

    private static void createFile() {
        Scanner scanner = new Scanner(System.in);

        System.out.println("Enter the name of the file to create:");
        String filename = scanner.nextLine();

        try {
            File file = new File(filename);

            if (file.createNewFile()) {
                System.out.println("File created: " + file.getAbsolutePath());
            } else {
                System.out.println("File already exists.");
            }

            FileWriter writer = new FileWriter(file);

            System.out.println("Enter text to write to the file:");
            String text = scanner.nextLine();

            writer.write(text);
            writer.close();

            System.out.println("Text written to file.");
        } catch (IOException e) {
            System.out.println("Error creating file: " + e.getMessage());
        }
    }

    private static void openFile() {
        Scanner scanner = new Scanner(System.in);

        System.out.println("Enter the name of the file to open:");
        String filename = scanner.nextLine();

        try {
            File file = new File(filename);

            if (file.exists()) {
                FileReader reader = new FileReader(file);
                BufferedReader bufferedReader = new BufferedReader(reader);

                String line;

                System.out.println("File contents:");
                while ((line = bufferedReader.readLine()) != null) {
                    System.out.println(line);
                }

                reader.close();
            } else {
                System.out.println("File does not exist.");
            }
        } catch (IOException e) {
            System.out.println("Error reading file: " + e.getMessage());
        }
    }
}

这个简单的记事本程序提供了三个选项：创建新文件、打开现有文件或退出程序。如果选择创建新文件，程序会要求用户输入文件名和要写入文件的文本。如果选择打开现有文件，程序会要求用户输入文件名并显示文件内容。