Mastering Java FileReader: Comprehensive Guide & Practical Examples

Java FileReader Class

This guide walks you through Java’s FileReader, covering its constructors, key methods, and practical examples.

The FileReader class in the java.io package reads character data from files. It extends InputStreamReader and supports different character encodings.

Before diving into FileReader, make sure you understand Java’s File API.

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Creating a FileReader

First, import the class:

import java.io.FileReader;

1. By file name

FileReader input = new FileReader("path/to/file.txt");

Creates a reader that opens the specified file.

2. By File object

File fileObj = new File("path/to/file.txt");
FileReader input = new FileReader(fileObj);

3. Specifying a charset (Java 11+)

FileReader input = new FileReader("path/to/file.txt", StandardCharsets.UTF_8);

Using Charset allows you to read files with the desired encoding.

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Key Methods of FileReader

FileReader implements all methods from Reader and adds its own functionality.

read() Method

• read() – reads a single character.
• read(char[] array) – fills the array with characters.
• read(char[] array, int offset, int length) – reads length characters into the array starting at offset.

Example: Reading input.txt containing “This is a line of text inside the file.”

import java.io.FileReader;
class Main {
    public static void main(String[] args) {
        char[] buffer = new char[100];
        try (FileReader reader = new FileReader("input.txt")) {
            int readCount = reader.read(buffer);
            System.out.println("Data in the file:");
            System.out.println(new String(buffer, 0, readCount));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Output

Data in the file:
This is a line of text inside the file.

Note: Place input.txt in the current working directory.

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getEncoding() Method

Retrieve the charset used by the reader:

import java.io.FileReader;
import java.nio.charset.StandardCharsets;
class Main {
    public static void main(String[] args) {
        try {
            FileReader defaultReader = new FileReader("input.txt");
            FileReader utf8Reader = new FileReader("input.txt", StandardCharsets.UTF_8);
            System.out.println("Default encoding: " + defaultReader.getEncoding());
            System.out.println("UTF-8 encoding: " + utf8Reader.getEncoding());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Output

Default encoding: Cp1252
UTF-8 encoding: UTF-8

When a charset is specified, getEncoding() returns that charset; otherwise it reflects the platform default.

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close() Method

Always close the reader after use. The try-with-resources statement shown above handles this automatically.

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Additional FileReader Methods

Method	Description
ready()	Indicates whether the stream is ready to be read.
mark()	Marks the current position in the stream.
reset()	Resets the stream to the most recent mark.

For more details, refer to the official Java FileReader documentation.