How does Java I/O stream read and write files?

Java I/O streams facilitate file processing: Reading files: Use a FileInputStream object to create an input stream. Use the read() method to read the file contents into a byte array. Iterate over the byte array and print the contents. Writing to a file: Use a FileOutputStream object to create an output stream. Use the write() method to write a string to a file. Practical case: Use FileInputStream and Scanner to read specific lines from a file. Read the file line by line and compare the line numbers. Print the contents of the line matching the line number.

Java I/O streams: reading and writing files

Introduction

Java I/O streams provide a convenient way to process files. We can read and write files using streams.

Read and write files

1. Read files

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

public class ReadFile {

    public static void main(String[] args) {
        try {
            // 创建一个 FileInputStream 对象
            FileInputStream fis = new FileInputStream(new File("file.txt"));

            // 创建一个字节数组
            byte[] data = new byte[1024];

            // 读取文件内容到字节数组
            int readBytes = fis.read(data);

            // 循环遍历字节数组并打印文件内容
            for (int i = 0; i < readBytes; i++) {
                System.out.print((char) data[i]);
            }

            // 关闭文件输入流
            fis.close();

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

2. Write files

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;

public class WriteFile {

    public static void main(String[] args) {
        try {
            // 创建一个 FileOutputStream 对象
            FileOutputStream fos = new FileOutputStream(new File("file.txt"));

            // 将字符串写入文件
            String data = "This is a sample text.";
            fos.write(data.getBytes());

            // 关闭文件输出流
            fos.close();

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

Practical case

Read specific lines from a file

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.Scanner;

public class ReadSpecificLine {

    public static void main(String[] args) {
        try {
            // 创建一个 FileInputStream 对象
            FileInputStream fis = new FileInputStream(new File("file.txt"));

            // 创建一个 Scanner 对象
            Scanner scanner = new Scanner(fis);

            // 输入要读取的行号
            int lineNumber = 5;

            // 逐行读取文件
            int currentLine = 1;
            while (scanner.hasNextLine()) {
                String line = scanner.nextLine();

                // 如果当前行号等于要读取的行号，则打印该行
                if (currentLine == lineNumber) {
                    System.out.println(line);
                }

                currentLine++;
            }

            // 关闭文件输入流
            fis.close();

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

The above is the detailed content of How does Java I/O stream read and write files?. For more information, please follow other related articles on the PHP Chinese website!