Java I/O Basics

The java.io package provides a robust set of classes and methods for performing input and output operations in Java. These operations include reading from and writing to files, handling streams, and managing file metadata.

In this section, we’ll explore:

• The File class for representing file and directory paths.
• Key classes for reading and writing files:
  • FileReader and FileWriter.
  • BufferedReader and BufferedWriter.

---

The File Class

The File class in Java represents file and directory pathnames. It allows you to perform operations such as creating, deleting, and checking the existence of files or directories.

Common Methods of the File Class

Method	Description
createNewFile()	Creates a new empty file.
delete()	Deletes the file or directory.
exists()	Checks if the file or directory exists.
isDirectory()	Checks if the pathname is a directory.
listFiles()	Lists all files in a directory.

Example: Using the File Class

import java.io.File;
import java.io.IOException;

public class FileExample {
    public static void main(String[] args) {
        // Create a File object for a specific path
        File file = new File("example.txt");

        try {
            // Create a new file
            if (file.createNewFile()) {
                System.out.println("File created: " + file.getName());
            } else {
                System.out.println("File already exists.");
            }
        } catch (IOException e) {
            System.out.println("Error: " + e.getMessage());
        }

        // Check if the file exists
        if (file.exists()) {
            System.out.println("File exists at path: " + file.getAbsolutePath());
        }

        // Delete the file
        if (file.delete()) {
            System.out.println("File deleted successfully.");
        } else {
            System.out.println("Failed to delete the file.");
        }
    }
}

Output:

File created: example.txt
File exists at path: /path/to/example.txt
File deleted successfully.

Explanation:

• The File class is used to create, check, and delete a file.
• The createNewFile() method creates a new file if it doesn’t already exist.

---

FileReader and FileWriter

The FileReader and FileWriter classes are used for reading from and writing to text files.

Example: Writing to a File Using FileWriter

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

public class FileWriterExample {
    public static void main(String[] args) {
        try (FileWriter writer = new FileWriter("output.txt")) {
            writer.write("Hello, World!");
            System.out.println("Data written to file.");
        } catch (IOException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
}

Output:

Data written to file.

Explanation:

• The FileWriter class writes text to a file.
• The try-with-resources statement ensures that the file is closed automatically after writing.

Example: Reading from a File Using FileReader

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

public class FileReaderExample {
    public static void main(String[] args) {
        try (FileReader reader = new FileReader("output.txt")) {
            int content;
            while ((content = reader.read()) != -1) {
                System.out.print((char) content);
            }
        } catch (IOException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
}

Output:

Hello, World!

Explanation:

• The FileReader class reads text from a file character by character.
• The read() method returns -1 when the end of the file is reached.

---

BufferedReader and BufferedWriter

The BufferedReader and BufferedWriter classes provide efficient ways to read and write text files by buffering data.

Example: Writing to a File Using BufferedWriter

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

public class BufferedWriterExample {
    public static void main(String[] args) {
        try (BufferedWriter writer = new BufferedWriter(new FileWriter("output.txt"))) {
            writer.write("Hello, World!");
            writer.newLine(); // Add a new line
            writer.write("This is a buffered writer example.");
            System.out.println("Data written to file.");
        } catch (IOException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
}

Output:

Data written to file.

Explanation:

• The BufferedWriter class improves performance by buffering data before writing it to the file.
• The newLine() method adds a platform-independent newline character.

Example: Reading from a File Using BufferedReader

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

public class BufferedReaderExample {
    public static void main(String[] args) {
        try (BufferedReader reader = new BufferedReader(new FileReader("output.txt"))) {
            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }
        } catch (IOException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
}

Output:

Hello, World!
This is a buffered writer example.

Explanation:

• The BufferedReader class reads text from a file line by line.
• The readLine() method returns null when the end of the file is reached.

---

Key Takeaways

• The File class is used to represent file and directory paths and perform operations like creating, deleting, and checking file existence.
• The FileReader and FileWriter classes are used for reading from and writing to text files.
• The BufferedReader and BufferedWriter classes improve performance by buffering data during read/write operations.
• Use try-with-resources to ensure that files are closed automatically after use.