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Concept of Objects: State, Behavior & Identity of an object

The concept of objects is fundamental to object-oriented programming (OOP), and it revolves around three key aspects: state, behavior, and identity.


Definition: For any given moment, the state of an object is formed from its characteristics.
Example: The state of ‘car’ can include properties like color, speed, fuel level and present gear.


Definition: This is a terminology that refers to the actions or methods that are performed by an object. They describe how the given object relates with others or its environment.

Example: Behaviors for cars can include accelerate, brake, changeGear, turnLeft.


Definition: An object’s identity is what separates it from other objects. It helps differentiate between multiple instances of the same class in the system.

Example: Every car on the road has certain unique identity such as a license plate number or Vehicle Identification Number (VIN).

Key Points:

  • Encapsulation: Objects encapsulate both state and behavior. The object encapsulates the internal state and uses methods to control access to it, promoting data security and integrity.
  • Abstraction: Objects make real-world things seem less real by modeling their most important traits and interactions. This lets developers focus on what is important and ignore the details that are not necessary.
  • Inheritance: Through inheritance, objects can inherit attributes and behaviors from other objects, fostering code reuse and creating a hierarchical structure.
  • Polymorphism: Objects of different classes can be treated as objects of a common base class through polymorphism, enabling flexibility and extensibility in the code.
Categories OOP