📁 Java File Handling (Important ⭐)

File Handling allows Java programs to create, read, write, update, and delete files.

It is useful when your application needs to work with data stored outside the program.

Examples:

• 📄 Reading a text file

• 📝 Writing data to a file

• 📊 Processing CSV files

• 📋 Creating reports

• 💾 Storing application data

✅ 1️⃣ What is File Handling?

File Handling means performing operations on files using Java.

Common operations:

Create

Read

Write

Append

Delete

Java provides several classes for this purpose.

🔹 2️⃣ Important File Handling Classes

Some commonly used classes are:

File

FileReader

FileWriter

BufferedReader

BufferedWriter

Each has a different purpose.

🔹 3️⃣ File Class

The "File" class is used to work with file and directory information.

Example:

import java.io.File;

class FileDemo {
    public static void main(String[] args) {

        File file = new File("data.txt");

        System.out.println(file.exists());
    }
}

If "data.txt" exists:

true

Otherwise:

false

🔹 4️⃣ Creating a File

You can create a new file using "createNewFile()".

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

class CreateFile {
    public static void main(String[] args) throws IOException {

        File file = new File("data.txt");

        if (file.createNewFile()) {
            System.out.println("File created");
        } else {
            System.out.println("File already exists");
        }
    }
}

🔹 5️⃣ Writing to a File

"FileWriter" can be used to write text into a file.

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

class WriteFile {
    public static void main(String[] args) throws IOException {

        FileWriter writer = new FileWriter("data.txt");

        writer.write("Welcome to Java");

        writer.close();
    }
}

The file will contain:

Welcome to Java

🔹 6️⃣ Appending Data

By default, "FileWriter" can overwrite existing content.

To append instead:

FileWriter writer = new FileWriter("data.txt", true);

writer.write("\nLearning File Handling");

writer.close();

Now the file contains:

Welcome to Java
Learning File Handling

🔹 7️⃣ Reading a File

"FileReader" can read characters from a file.

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

class ReadFile {
    public static void main(String[] args) throws IOException {

        FileReader reader = new FileReader("data.txt");

        int character;

        while ((character = reader.read()) != -1) {
            System.out.print((char) character);
        }

        reader.close();
    }
}

Output:

Welcome to Java
Learning File Handling

⭐ 8️⃣ BufferedReader

"BufferedReader" is useful for reading text efficiently, especially line by line.

Example:

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

class ReadFile {
    public static void main(String[] args) throws IOException {

        BufferedReader reader =
            new BufferedReader(new FileReader("data.txt"));

        String line;

        while ((line = reader.readLine()) != null) {
            System.out.println(line);
        }

        reader.close();
    }
}

👉 "readLine()" reads one complete line at a time.

🔹 9️⃣ BufferedWriter

"BufferedWriter" can efficiently write text to a file.