Java函数如何进行文件读取和写入？

Java中可以使用多种方式进行文件的读取和写入操作，以下是其中几种常用的方法：

1. 使用File类进行文件读取和写入：

   // 文件读取
   File file = new File("filename.txt");
   try {
       FileReader fileReader = new FileReader(file);
       BufferedReader bufferedReader = new BufferedReader(fileReader);
       String line;
       while ((line = bufferedReader.readLine()) != null) {
           System.out.println(line);
       }
       bufferedReader.close();
   } catch (IOException e) {
       e.printStackTrace();
   }
   
   // 文件写入
   try {
       FileWriter fileWriter = new FileWriter(file, true);
       BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
       bufferedWriter.write("Hello, World!");
       bufferedWriter.newLine();
       bufferedWriter.close();
   } catch (IOException e) {
       e.printStackTrace();
   }
   

2. 使用Scanner进行文件读取：

   // 文件读取
   File file = new File("filename.txt");
   try {
       Scanner scanner = new Scanner(file);
       while (scanner.hasNextLine()) {
           String line = scanner.nextLine();
           System.out.println(line);
       }
       scanner.close();
   } catch (FileNotFoundException e) {
       e.printStackTrace();
   }
   
   // 文件写入
   try {
       FileWriter fileWriter = new FileWriter(file, true);
       BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
       bufferedWriter.write("Hello, World!");
       bufferedWriter.newLine();
       bufferedWriter.close();
   } catch (IOException e) {
       e.printStackTrace();
   }
   

3. 使用InputStream和OutputStream进行文件读取和写入：

   // 文件读取
   try {
       InputStream inputStream = new FileInputStream("filename.txt");
       int data;
       while ((data = inputStream.read()) != -1) {
           System.out.println(data);
       }
       inputStream.close();
   } catch (IOException e) {
       e.printStackTrace();
   }
   
   // 文件写入
   try {
       OutputStream outputStream = new FileOutputStream("filename.txt", true);
       String str = "Hello, World!";
       byte[] bytes = str.getBytes();
       outputStream.write(bytes);
       outputStream.close();
   } catch (IOException e) {
       e.printStackTrace();
   }
   

4. 使用BufferedReader和BufferedWriter进行文件读取和写入：

   // 文件读取
   try {
       FileReader fileReader = new FileReader("filename.txt");
       BufferedReader bufferedReader = new BufferedReader(fileReader);
       String line;
       while ((line = bufferedReader.readLine()) != null) {
           System.out.println(line);
       }
       bufferedReader.close();
   } catch (IOException e) {
       e.printStackTrace();
   }
   
   // 文件写入
   try {
       FileWriter fileWriter = new FileWriter("filename.txt", true);
       BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
       bufferedWriter.write("Hello, World!");
       bufferedWriter.newLine();
       bufferedWriter.close();
   } catch (IOException e) {
       e.printStackTrace();
   }
   

以上是几种常用的文件读取和写入方法，根据实际需求选择适合的方法进行文件操作。