Java FileReader and FileWriter Classes

When working with files in Java, FileReader and FileWriter provide a convenient way to read and write text data using character streams. These classes are specifically designed for handling character files.

1. Class Hierarchy#

java.lang.Object
  ↳ java.io.Reader
       ↳ java.io.FileReader

java.lang.Object
  ↳ java.io.Writer
       ↳ java.io.FileWriter

• FileReader extends Reader
• FileWriter extends Writer

2. FileReader Class#

● Constructors#

FileReader(String fileName)
FileReader(File file)

These constructors open a file for reading. If the file doesn't exist, a FileNotFoundException is thrown.

● Example: Reading from a file using FileReader#

import java.io.*;

public class FileReaderExample {
    public static void main(String[] args) {
        try (FileReader reader = new FileReader("example.txt")) {
            int ch;
            while ((ch = reader.read()) != -1) {
                System.out.print((char) ch); // Print each character one by one
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Output (if example.txt contains "Hello World"):#

Hello World

● int read()#

Reads a single character.

● int read(char[] cbuf, int offset, int length)#

Reads characters into a portion of an array.

import java.io.*;

public class FileReaderReadArray {
    public static void main(String[] args) {
        char[] buffer = new char[100];
        try (FileReader reader = new FileReader("example.txt")) {
            int charsRead = reader.read(buffer, 0, buffer.length);
            System.out.println("Characters read: " + new String(buffer, 0, charsRead));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Output:#

Characters read: Hello World

● void close()#

Closes the reader. Automatically handled with try-with-resources.

import java.io.*;

public class FileReaderCloseExample {
    public static void main(String[] args) {
        FileReader reader = null;
        try {
            reader = new FileReader("example.txt");
            System.out.println("Reader opened.");
            reader.read();
            reader.close(); // manually closing
            System.out.println("Reader closed.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Output:#

Reader opened.
Reader closed.

3. FileWriter Class#

● Constructors#

FileWriter(String fileName)
FileWriter(String fileName, boolean append)
FileWriter(File file)
FileWriter(File file, boolean append)

These constructors create a file if it doesn't exist and optionally allow appending.

● Example: Writing to a file using FileWriter#

import java.io.*;

public class FileWriterExample {
    public static void main(String[] args) {
        try (FileWriter writer = new FileWriter("output.txt")) {
            writer.write("Hello Java");
            System.out.println("Data written successfully.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Output:#

Data written successfully.

File output.txt will contain:

Hello Java

● void write(int c)#

Writes a single character.

import java.io.*;

public class FileWriterWriteChar {
    public static void main(String[] args) {
        try (FileWriter writer = new FileWriter("output.txt")) {
            writer.write(65); // Writes 'A'
            System.out.println("Single character written.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Output:#

Single character written.

File content:

A

● void write(char[] cbuf, int off, int len)#

Writes a portion of a character array.

import java.io.*;

public class FileWriterCharArray {
    public static void main(String[] args) {
        char[] data = "Welcome to Java".toCharArray();
        try (FileWriter writer = new FileWriter("output.txt")) {
            writer.write(data, 0, data.length);
            System.out.println("Char array written.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Output:#

Char array written.

● void write(String str, int off, int len)#

Writes a portion of a string.

import java.io.*;

public class FileWriterWriteString {
    public static void main(String[] args) {
        String msg = "Java FileWriter Demo";
        try (FileWriter writer = new FileWriter("output.txt")) {
            writer.write(msg, 5, msg.length() - 5); // Write "FileWriter Demo"
            System.out.println("String written with offset.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Output:#

String written with offset.

File content:

FileWriter Demo

● void flush()#

Flushes the stream — forces any buffered output to be written.

import java.io.*;

public class FileWriterFlushExample {
    public static void main(String[] args) {
        try (FileWriter writer = new FileWriter("output.txt")) {
            writer.write("Flush Example");
            writer.flush(); // Force write
            System.out.println("Data flushed.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Output:#

Data flushed.

● void close()#

Closes the writer. Automatically done by try-with-resources.

import java.io.*;

public class FileWriterCloseExample {
    public static void main(String[] args) {
        FileWriter writer = null;
        try {
            writer = new FileWriter("output.txt");
            writer.write("Close Example");
            writer.close();
            System.out.println("Writer closed.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Output:#

Writer closed.

Conclusion#

In this blog, we explored the FileReader and FileWriter classes which are ideal for reading and writing character-based files. We demonstrated each method with practical examples and outputs to make the concepts beginner-friendly.

Next, we’ll dive into BufferedReader and BufferedWriter classes for more efficient file handling using buffers.