Java > File I/O

File I/O in Java

File I/O (Input/Output) in Java is essential for reading data from and writing data to files. Java provides various classes in the java.io and java.nio packages for file handling.

Common File I/O Operations

Operation	Package	Class	Method
Create File	java.io	File	createNewFile()
Read File	java.io	FileReader	read()
Write to File	java.io	FileWriter	write()
Buffered Read	java.io	BufferedReader	readLine()
Append to File	java.io	FileWriter	write() with true flag
Delete File	java.io	File	delete()

Creating a File

To create a file, you can use the File class.

Example: Creating a File

package com.vvsk.fullstack.files;

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

public class CreateFileExample {
    public static void main(String[] args) {
        try {
            File file = new File("example.txt");
            if (file.createNewFile()) {
                System.out.println("File created: " + file.getName());
            } else {
                System.out.println("File already exists.");
            }
        } catch (IOException e) {
            System.out.println("An error occurred while creating the file.");
            e.printStackTrace();
        }
    }
}

Writing to a File

For writing content to a file, use FileWriter or BufferedWriter.

Example: Writing to a File

package com.vvsk.fullstack.files;

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

public class WriteFileExample {
    public static void main(String[] args) {
        try {
            FileWriter writer = new FileWriter("example.txt");
            writer.write("Hello, this is a sample text written to the file.");
            writer.close();
            System.out.println("Successfully wrote to the file.");
        } catch (IOException e) {
            System.out.println("An error occurred while writing to the file.");
            e.printStackTrace();
        }
    }
}

Reading from a File

For reading data from a file, you can use FileReader, BufferedReader, or Scanner.

Example: Reading a File Using FileReader

package com.vvsk.fullstack.files;

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

public class ReadFileExample {
    public static void main(String[] args) {
        try (FileReader reader = new FileReader("example.txt")) {
            int character;
            while ((character = reader.read()) != -1) {
                System.out.print((char) character);
            }
        } catch (IOException e) {
            System.out.println("An error occurred while reading the file.");
            e.printStackTrace();
        }
    }
}

Combining Read and Write with Exception Handling

Using try-with-resources is the best practice for automatic resource management.

Example: Read and Write with Exception Handling

package com.vvsk.fullstack.files;

import java.io.*;

public class FileReadWriteExample {
    public static void main(String[] args) {
        String filePath = "example.txt";

        // Writing to file
        try (FileWriter writer = new FileWriter(filePath)) {
            writer.write("This text is both written and read using Java File I/O.");
            System.out.println("Data written successfully.");
        } catch (IOException e) {
            System.out.println("Error writing to file: " + e.getMessage());
        }

        // Reading from file
        try (BufferedReader reader = new BufferedReader(new FileReader(filePath))) {
            String line;
            System.out.println("Reading content from file:");
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }
        } catch (IOException e) {
            System.out.println("Error reading from file: " + e.getMessage());
        }
    }
}

Key Classes in Java File I/O

Class	Description
File	Used to create, delete, and inspect file properties.
FileWriter	Used for writing character data to files.
FileReader	Used for reading character data from files.
BufferedReader	Efficient for reading large text data.
PrintWriter	Provides efficient text formatting during writing.
Scanner	Flexible for reading input from files.

Best Practices for File I/O

✅ Always close file resources using try-with-resources or .close().
✅ Handle exceptions like IOException and FileNotFoundException properly.
✅ Use Buffered classes for better performance when handling large files.

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