Text File I/O in Java Using Character Streams

Java provides character-stream classes in the java.io package to read and write text-based files. These classes are ideal for working with:

.txt
.csv
.json
.xml
.log

Below are the three main classes used for text file operations:

1. FileReader (Reading Text Files Character-by-Character)

FileReader is a character-input stream used to read text files one character at a time.

Key Features

Reads Unicode characters
Best for small-size files
Simple and easy to use
Not optimized for large files

Example

import java.io.FileReader;

public class FileReaderExample {
    public static void main(String[] args) {
        try (FileReader fr = new FileReader("input.txt")) {
            int ch;
            while ((ch = fr.read()) != -1) {
                System.out.print((char) ch);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

2. BufferedReader (Efficient Text Reading)

BufferedReader wraps a FileReader to provide fast and efficient reading using an internal buffer.

Key Features

Reads text line-by-line
Much faster than FileReader
Great for large files, logs, CSVs

Example

import java.io.BufferedReader;
import java.io.FileReader;

public class BufferedReaderExample {
    public static void main(String[] args) {
        try (BufferedReader br = new BufferedReader(new FileReader("input.txt"))) {
            String line;
            while ((line = br.readLine()) != null) {
                System.out.println(line);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Important Methods

read() – reads a single character
readLine() – reads entire line
close() – closes the stream

3. FileWriter (Writing Text Files)

FileWriter is a character-output stream used to write data into text files.

Key Features

Writes text/characters
Overwrites file by default
Can append to existing file

Example

import java.io.FileWriter;

public class FileWriterExample {
    public static void main(String[] args) {
        try (FileWriter fw = new FileWriter("output.txt")) {
            fw.write("Hello, Java!\\n");
            fw.write("Writing using FileWriter.");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Append Mode

FileWriter fw = new FileWriter("output.txt", true);
fw.write("\\nAppending new data...");
fw.close();

4. BufferedWriter (Optional but Important)

BufferedWriter wraps a FileWriter and writes text efficiently using buffering.

Why Use BufferedWriter?

Faster than FileWriter alone
Supports newLine() method
Ideal for writing large text files

Example

import java.io.BufferedWriter;
import java.io.FileWriter;

public class BufferedWriterExample {
    public static void main(String[] args) {
        try (BufferedWriter bw = new BufferedWriter(new FileWriter("output.txt"))) {
            bw.write("Hello World!");
            bw.newLine();
            bw.write("Writing using BufferedWriter.");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

5. Full Example (Copy File using Character Streams)

import java.io.*;

public class CopyFile {
    public static void main(String[] args) {
        try (FileReader fr = new FileReader("source.txt");
             FileWriter fw = new FileWriter("destination.txt")) {

            int ch;
            while ((ch = fr.read()) != -1) {
                fw.write(ch);
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

When to Use What?

Class	Best Used For	Speed	Notes
FileReader	Reading characters	Slow	Good for small files
BufferedReader	Reading lines, large files	Fast	Most preferred
FileWriter	Writing characters	Medium	Overwrites file
BufferedWriter	Efficient writing	Fast	Supports newLine()

Points to Remember

FileReader → Reads characters one-by-one
BufferedReader → Reads text efficiently (best for large files)
FileWriter → Writes characters to a file
BufferedWriter → Writes text faster using a buffer
Use try-with-resources for automatic closing
Use append mode when you don't want to overwrite