Introduction to Java I/O Libraries

Java Input and Output (I/O) libraries provide a set of powerful tools that let you read data from and write data to a variety of sources. These sources include files on your computer, network connections, user input, and memory buffers.

Java I/O libraries are essential because:

• They allow you to save and retrieve information from files;
• They help you process user input and output in console applications;
• They support communication with external systems, such as web servers or databases;
• They make it possible to manage large data streams efficiently.

You use I/O classes and methods to perform common tasks like reading text from a file, writing results to a report, or transferring data over the internet. The Java standard library organizes these tools into clear, easy-to-use packages such as java.io and java.nio.

Understanding Java I/O is crucial for building real-world applications that interact with files, users, or networks. In this chapter, you will learn how to use these libraries to handle data safely and efficiently.

Common Java I/O Classes

Java provides several classes in the java.io package to handle input and output operations with files and streams. Understanding these classes helps you read from and write to files efficiently.

FileReader and FileWriter

• FileReader: reads character data from files;
• FileWriter: writes character data to files.

Use these classes when working with text files. They handle basic character-based file operations.

Example usage:

FileReader reader = new FileReader("input.txt");
FileWriter writer = new FileWriter("output.txt");

BufferedReader and BufferedWriter

• BufferedReader: wraps around a Reader (like FileReader) to read text efficiently by buffering characters; provides convenient methods such as readLine();
• BufferedWriter: wraps around a Writer (like FileWriter) to write text efficiently by buffering characters; supports writing entire lines with newLine().

Buffered classes improve performance, especially for large files or repeated read/write operations.

Example usage:

BufferedReader bufferedReader = new BufferedReader(new FileReader("input.txt"));
BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter("output.txt"));

Typical Workflow

1. Open a file using FileReader or FileWriter;
2. Wrap it with BufferedReader or BufferedWriter for better performance;
3. Perform read or write operations;
4. Close all streams to release resources.

These classes form the foundation for text file I/O in Java. Always close streams in a finally block or use try-with-resources to prevent resource leaks.