Java File Io — Free Java Tutorial

TL;DR: Learn Java File Io in Java with a free, beginner-friendly tutorial, examples and practice for Indian students on Syllab.in.

Java File Io in Java

Java's java.io and java.nio packages provide classes for reading and writing files. The modern NIO.2 API (Files, Paths) from Java 7+ is cleaner and more powerful.

For reading: Files.readAllLines(), Files.readString() (Java 11+), BufferedReader for large files. For writing: Files.writeString(), Files.write(), BufferedWriter.

Always use try-with-resources to auto-close streams: try (BufferedReader br = ...) { } — ensures the file is closed even if an exception occurs.

Path (java.nio.file.Path) represents a file path in a platform-independent way. Paths.get() creates a Path. Files class provides static utility methods for common operations.

import java.nio.file.*;
import java.io.*;

// Read all lines
List<String> lines = Files.readAllLines(Path.of("file.txt"));

// Write string
Files.writeString(Path.of("out.txt"), "Hello World");

// Append to file
Files.writeString(path, "more text", StandardOpenOption.APPEND);

// BufferedReader for large files
try (BufferedReader br = new BufferedReader(new FileReader("big.txt"))) {
    String line;
    while ((line = br.readLine()) != null) { process(line); }
}

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