Question

What is the difference between public, protected and private keywords?

Short answer

Public allows access from anywhere, protected allows access within the same package and subclasses, and private restricts access to the same class.

Step-by-step solution

Understanding Access Modifiers

In object-oriented programming, access modifiers are keywords used to set the accessibility of classes, methods, and other members. The main access modifiers are public, protected, and private.

Define 'Public' Modifier

The 'public' modifier means that the member or class is accessible from any other class. It does not have any restricted access, allowing members to be accessed from any part of the program.

Define 'Protected' Modifier

The 'protected' modifier allows access to members by classes in the same package and subclasses. This means it restricts the visibility to the class itself and any subclasses or classes in the same package, not allowing access by unrelated classes.

Define 'Private' Modifier

The 'private' modifier specifies that the member is accessible only within the class it is declared. It provides the most restrictive access, ensuring that the member cannot be accessed from outside the class definition.

Key concepts

Object-Oriented Programming

Object-oriented programming (OOP) is a programming paradigm that uses objects to model real-world entities and relationships. These objects have attributes, known as properties, and behaviors, known as methods. OOP aims to make software design more intuitive and manageable by grouping related tasks.

• Using classes and objects, programmers can create modular and reusable code.
• This approach supports encapsulation, inheritance, and polymorphism, which are key principles of OOP.

Encapsulation, a fundamental OOP concept, involves bundling data (attributes) and methods (behaviors) that act on the data into a single unit, or class. Access modifiers play a crucial role in encapsulation by controlling the level of access other classes have to a class's data and methods.

Public Modifier

The 'public' modifier is one of the most permissive access levels in object-oriented programming. When a class member is declared public, it means that member is accessible by any other class, irrespective of its package or subclass.

• Public members allow open access, making them usable throughout your code and even in other packages.
• While public visibility provides flexibility, it may lead to security concerns because public data can be accessed and modified by any external class.

Using the 'public' modifier appropriately is essential, as it provides the highest level of accessibility that could potentially compromise the integrity of your data if not handled wisely.

Protected Modifier

A step down from public, the 'protected' modifier offers a balance between accessibility and protection. This modifier allows class members to be accessible within their own class, subclasses, and other classes in the same package.

• 'Protected' members help promote reuse by enabling subclasses to access necessary components from parent classes.
• However, they still offer a layer of privacy from unrelated classes, which prevents potential misuse.

Choosing the 'protected' modifier is often a good choice for scenarios where you want to shield class members from the outside world, while still enabling a controlled level of accessibility for inheritance and package-level collaboration.

Private Modifier

The 'private' modifier provides the most restrictive level of access in object-oriented programming. When a class member is declared private, it can only be accessed within its own class.

• Private members safeguard the internal data of a class from outside interference, maintaining the integrity of the class by preventing unauthorized modifications.
• This access level is ideal for variables and methods which are used only internally within the class and should not be exposed.

Choosing to declare variables and methods as private is a crucial part of implementing the encapsulation principle, ensuring that sensitive data and computations are protected from external forces.