Java I/O Character Streams

Character streams in Java are designed to handle the input and output of characters. They automatically handle the translation to and from the local character set, making them ideal for processing text data. The primary classes for character streams are Reader and Writer and their subclasses.

Table of Contents

1. Introduction
2. Character Stream Classes
   • Reader
   • Writer
3. Examples
   • Reading Characters from a File
   • Writing Characters to a File
   • Copying a Text File
4. Conclusion

Introduction

Character streams are used for reading and writing text data (characters). Unlike byte streams, character streams are specifically designed for handling 16-bit Unicode characters, making them suitable for text processing. They automatically handle character encoding and decoding, which is essential for internationalization.

Character Stream Classes

Reader

The Reader class is the abstract superclass for all classes that read character streams. It provides methods for reading characters, arrays of characters, and lines.

Common Reader subclasses:

• FileReader
• StringReader
• BufferedReader

Writer

The Writer class is the abstract superclass for all classes that write character streams. It provides methods for writing characters, arrays of characters, and strings.

Common Writer subclasses:

• FileWriter
• StringWriter
• BufferedWriter

Examples

Reading Characters from a File

The following example demonstrates how to read characters from a file using FileReader.

Example

import java.io.FileReader;
import java.io.IOException;

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

Explanation:

• FileReader is used to read characters from a file named input.txt.
• The read() method reads one character at a time and returns -1 when the end of the file is reached.
• The character data is printed to the console.

Writing Characters to a File

The following example demonstrates how to write characters to a file using FileWriter.

Example

import java.io.FileWriter;
import java.io.IOException;

public class FileWriterExample {
    public static void main(String[] args) {
        try (FileWriter fw = new FileWriter("output.txt")) {
            String content = "Hello, World!";
            fw.write(content);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Explanation:

• FileWriter is used to write characters to a file named output.txt.
• The write() method writes the string content to the file.

Copying a Text File

The following example demonstrates how to copy a text file using FileReader and FileWriter.

Example

import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class CopyTextFileExample {
    public static void main(String[] args) {
        try (FileReader fr = new FileReader("input.txt");
             FileWriter fw = new FileWriter("output.txt")) {
            int charData;
            while ((charData = fr.read()) != -1) {
                fw.write(charData);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Explanation:

• FileReader reads characters from input.txt.
• FileWriter writes characters to output.txt.
• Each character read from the input file is written to the output file.

Using Buffered Character Streams

Buffered streams can significantly improve performance when reading from or writing to files by reducing the number of I/O operations. The following example demonstrates how to use BufferedReader and BufferedWriter to copy a text file efficiently.

Example

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class BufferedCharacterStreamExample {
    public static void main(String[] args) {
        try (BufferedReader br = new BufferedReader(new FileReader("input.txt"));
             BufferedWriter bw = new BufferedWriter(new FileWriter("output.txt"))) {
            String line;
            while ((line = br.readLine()) != null) {
                bw.write(line);
                bw.newLine();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Explanation:

• BufferedReader reads lines of text from input.txt.
• BufferedWriter writes lines of text to output.txt.
• Each line read from the input file is written to the output file, followed by a new line.

Conclusion

Character streams in Java provide a way to handle the input and output of characters, making them ideal for text processing. They automatically handle the translation to and from the local character set, ensuring that text data is processed correctly. By understanding how to use Reader and Writer classes, along with their buffered counterparts, you can efficiently manage and process text data in your Java applications. The examples provided demonstrate basic usage, including reading from a file, writing to a file, and copying a text file.