Does it make a difference if I write "public class" instead of just "class"?

Yes, there’s an important difference between public class and just class in Java. Here’s what you need to know:

1. Accessibility Difference

public class: The class can be accessed from anywhere in your program (even from other packages/folders).

public class Main {  // Can be used everywhere
  public static void main(String[] args) {
    System.out.println("Hello!");
  }
}

class (no modifier): The class is only accessible within its own package/folder.

class Helper {  // Only usable in this package
  void doSomething() { ... }
}

2. File Naming Rule (For public Classes)

If you declare a class as public, the filename must match the class name.

• Name of the file containing public class Main { ... } should be Main.java.

• Name of the file containing public class MyProgram { ... } can't be Main.java.

3. When to Use Which?

• Use public for classes that need to be shared across your project (like Main).

• Use default (class without public) for helper classes that only one package uses.

// File: Main.java (Public, so filename matches)
public class Main {
  public static void main(String[] args) {
    Helper.help();  // Can only call if Helper is public or in same package
  }
}

// File: Helper.java (No 'public' = package-private)
class Helper {
  static void help() {
    System.out.println("Assisting...");
  }
}

Key Takeaway:

• public means anyone can use this class.

• No modifier means only my package/folder can use this class.