File I/O

n Java, we use "Streams" to move data. Imagine a water pipe: data flows from your program into a file, or from a file into your program.

The Modern Way: Files and Paths

Java has several ways to handle files. The oldest way (using File) is a bit clunky. Modern Java (since version 7/8) uses the java.nio.file package, which is much easier and more powerful.

We will use:

1. Paths.get(): To find the file location.

2. Files.writeString(): To save text easily.

3. Files.readString(): To pull text back into our program.

The Code Example:

import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.io.IOException;

public class FileIODemo {
    public static void main(String[] args) {
        String fileName = "myNote.txt";
        String contentToWrite = "Hello! This is a secret message stored in a file.\nJava is awesome!";

        // 1. Defining the Path
        Path path = Paths.get(fileName);

        try {
            // 2. Writing to the file (This creates the file if it doesn't exist)
            Files.writeString(path, contentToWrite);
            System.out.println("Success: File written to " + path.toAbsolutePath());

            System.out.println("--- Reading back from the file ---");

            // 3. Reading from the file
            String readContent = Files.readString(path);
            
            // Displaying what we found
            System.out.println("File Content:\n" + readContent);

        } catch (IOException e) {
            // File operations can fail (no permission, disk full), so we NEED try-catch
            System.out.println("An error occurred: " + e.getMessage());
        }
    }
}

Expected Output:

Success: File written to C:\Users\Current\Project\myNote.txt
--- Reading back from the file ---
File Content:
Hello! This is a secret message stored in a file.
Java is awesome!

File I/O is the first step toward building real software. You use it for:

• Settings/Preferences: Saving a user's "Dark Mode" choice.

• Logging: Keeping a record of when an error occurred.

• Data Storage: Saving a high score in a game or a list of tasks in a To-Do app.

Important: Always wrap File I/O in a try-catch block. Unlike some other errors, Java forces you to handle IOException because the computer's file system is unpredictable!