What are entities in object-oriented programming?

In the context of Object-Oriented Programming (OOP), an "entity" refers to an object or a thing that has a distinct and independent existence and that can be identified and manipulated in a software system. In OOP, entities are typically represented as instances of classes.

Here are some key points about entities in OOP:

1. Objects as Entities:

   • Entities are often modeled as objects. An object is an instance of a class and encapsulates both data (attributes) and behavior (methods).
   • For example, in a library system, entities could include objects like Book, Patron, Transaction, etc.

2. Attributes and Methods:

   • Entities have attributes that represent their characteristics or properties. These attributes are often modeled as variables within a class.
   • Entities also have methods, which represent the actions or behaviors associated with them. Methods are functions that can be performed by or on the entity.

3. Real-World Representation:

   • Entities in OOP are often designed to represent real-world objects or concepts. For instance, in a banking system, entities might include objects like Account, Customer, and Transaction.

4. Encapsulation:

   • Entities exhibit encapsulation, where data and methods related to an entity are bundled together within a class. Encapsulation helps in organizing and protecting the internal state of an object.

5. Relationships:

   • Entities in a system can have relationships with each other. These relationships define how different entities interact or collaborate.
   • For instance, in an online shopping system, the entities Product, Customer, and Order might have relationships such as a customer placing an order for a product.

6. Abstraction and Inheritance:

   • Abstraction involves simplifying complex systems by modeling classes based on common attributes and behaviors.
   • Inheritance allows entities to inherit attributes and behaviors from a more general class, promoting code reuse.

7. Polymorphism:

   • Polymorphism allows entities of different types to be treated as instances of a common base type, simplifying code and promoting flexibility.

Entities, in the context of OOP, are a fundamental concept for designing and implementing software systems. They help organize and structure code by representing the key components and their interactions within the system.