How do you read and write files in Java?

Table of Contents

• Introduction
• Reading Files in Java
  • Using FileReader and BufferedReader
    • Example of Reading a File
  • Explanation
• Writing Files in Java
  • Using FileWriter and BufferedWriter
    • Example of Writing to a File
  • Explanation
• Using Java NIO for File Operations
  • Example of Reading and Writing with NIO
  • Explanation
• Conclusion

Introduction

Reading and writing files are fundamental operations in Java that allow you to manage data efficiently. Java provides several classes in the I/O (Input/Output) package to facilitate file handling. This guide will explain how to read from and write to files in Java using various classes, providing practical examples to illustrate these operations.

Reading Files in Java

Using FileReader and BufferedReader

The FileReader class is used for reading character files. It can be combined with BufferedReader to read text efficiently. The BufferedReader class buffers characters for efficient reading, reducing the number of I/O operations.

Example of Reading a File

Here's how to read a file using FileReader and BufferedReader:

Explanation

• The BufferedReader reads text from "input.txt" line by line.
• The readLine() method returns a line of text, and the loop continues until the end of the file is reached (when readLine() returns null).
• The try-with-resources statement ensures that resources are closed automatically after use.

Writing Files in Java

Using FileWriter and BufferedWriter

The FileWriter class is used to write characters to a file. You can enhance its functionality by using it with BufferedWriter, which buffers the output to provide efficient writing.

Example of Writing to a File

Here's how to write to a file using FileWriter and BufferedWriter:

Explanation

• The BufferedWriter writes data to "output.txt".
• The write() method writes a string to the file, and newLine() adds a line break.
• The try-with-resources statement ensures proper closing of resources.

Using Java NIO for File Operations

Java also provides the NIO (New Input/Output) package, which offers more advanced file handling capabilities, including asynchronous I/O and better performance for large files.

Example of Reading and Writing with NIO

Here's an example using Files class from the NIO package to read and write files:

Explanation

• The Files.write() method writes bytes to "nioOutput.txt" in one call.
• The Files.readAllLines() method reads all lines from "nioInput.txt" into a list.
• The for-loop prints each line from the file.

Conclusion

Java provides robust mechanisms for reading and writing files, allowing developers to handle data efficiently. Using classes like FileReader, FileWriter, BufferedReader, and BufferedWriter provides simple and effective ways to perform file I/O operations. Additionally, the NIO package enhances file handling capabilities, making it suitable for more advanced requirements. Mastering these techniques is essential for any Java developer working with file operations.