Reading Files Character-by-Character with FileReader

Welcome to this lesson on reading files with FileReader in Java. Building upon our foundational knowledge of handling text files, this lesson will guide you through utilizing Java's java.io.FileReader to read files character by character. These methods are crucial for handling varying file sizes efficiently and managing memory use effectively. By the end of this lesson, you'll be able to read entire files, specific portions, and process files in manageable chunks, granting you flexible control over text data processing.

Before we jump into reading files, let's review the example file that we will work with:

Hi!
This file contains some sample example text to use to test how the read method works.
Let's do some programming!

This file contains multiple lines of varied lengths.

The FileReader class in Java is part of the java.io package and is designed for reading files as a stream of characters. It provides methods to open a file and read its contents character by character, which is helpful for detailed text processing. To read a file's entire content character by character, we open the file using FileReader and utilize the read() method, which reads the next character in the stream and returns its integer representation.

Here is how to read a file completely character by character using a loop:

import java.io.FileReader;
import java.io.IOException;
import java.nio.file.Path;
import java.nio.file.Paths;

public class Main {
    public static void main(String[] args) throws IOException {
        // Create a Path object for the specified file
        Path filePath = Paths.get("example.txt");

        // Open the file for reading with FileReader
        FileReader reader = new FileReader(filePath.toFile());

        // Variable to store the integer representation of the character being read
        int charInt;

        // Read each character from the file until end-of-file is reached
        while ((charInt = reader.read()) != -1) {
            // Cast the integer to a character and output it
            System.out.print((char) charInt);
        }
        
        // Close the FileReader to free system resources
        reader.close();
    }
}

To open the file, filePath.toFile() converts the Path object into a File object required by FileReader. The read() method reads a character from the file and returns its integer representation, which is then cast back to a character using (char). The loop continues until all characters have been read. It is crucial to close the FileReader after the operations to release system resources and prevent potential file locks.

The expected output is:

Hi!
This file contains some sample example text to use to test how the read method works.
Let's do some programming!

This approach suits situations where processing files one character at a time is necessary or preferred. It provides a straightforward way to read entire files while maintaining resource efficiency, making FileReader a versatile option for file manipulation in Java.