What is public?

Public is a keyword used in many programming languages as an access modifier. When something (a class, method, variable, or property) is declared public, it means that any other part of the program, or even other programs, can see and use it without restrictions.

Let's break it down

  • Access modifiers: These are keywords that control who can see or change a piece of code. Common ones are public, private, protected, and internal.
  • Public members: Anything marked public can be accessed from anywhere the code is visible.
  • Scope: Public can apply to whole classes, individual functions, or data fields.
  • Syntax example (Java): public class MyClass { public void doSomething() { } }

Why does it matter?

Public determines how you organize and protect your code. By choosing the right access level, you can hide internal details (encapsulation), prevent accidental misuse, and clearly define what parts of your code are meant to be used by others. It also affects how easy it is to build libraries and APIs that other developers can rely on.

Where is it used?

  • Java: Public classes, methods, and fields.
  • C#: Public classes, methods, properties, and events.
  • C++: Public sections in class definitions.
  • JavaScript (ES6 modules): Exported functions or classes act like public members.
  • APIs and SDKs: Public methods form the contract that external code calls.

Good things about it

  • Easy sharing: Makes it simple to expose functionality to other parts of a program or to external developers.
  • Clear contracts: Public members define a clean interface that tells users what they can rely on.
  • Reusability: Public classes and methods can be reused across multiple projects, saving time.
  • Interoperability: Enables different modules, services, or libraries to work together.

Not-so-good things

  • Loss of encapsulation: Overusing public can expose internal state, making the code harder to maintain.
  • Security risks: Sensitive data or critical functions left public may be accessed unintentionally or maliciously.
  • Versioning headaches: Changing a public API can break existing users, so it requires careful planning.
  • Increased coupling: Other code may become dependent on public members, reducing flexibility to refactor internally.