Software Engineering basics - Object-Oriented Design (OOD)

Object-Oriented Design (OOD)

Definition:
Object-Oriented Design is a method of designing software based on real-world concepts, using objects that encapsulate data and behavior. It focuses on modeling a system using classes, objects, inheritance, and polymorphism.

Think of it like designing a zoo: each animal is an object with properties (name, age) and behaviors (eat, sleep), and animals of the same type share a class blueprint.

Key Concepts of OOD

  1. Classes and Objects

    • Class: A blueprint for creating objects. Defines attributes (data) and methods (behavior).

    • Object: An instance of a class. Each object has its own state.

    • Example: class Car { color, speed; drive(); stop(); } → myCar = new Car()

  2. Encapsulation

    • Bundling data and methods together in a class.

    • Hides internal implementation from the outside world (access via public methods).

    • Example: Private variables with public getter/setter methods.

  3. Inheritance

    • Allows a class (child) to inherit properties and methods from another class (parent).

    • Promotes code reuse and hierarchical relationships.

    • Example: class ElectricCar extends Car { batteryCapacity; }

  4. Polymorphism

    • Objects can take many forms.

    • Two types:

      • Compile-time (Method Overloading): Same method name, different parameters.

      • Run-time (Method Overriding): Child class provides a specific implementation of a parent method.

    • Example: car.drive() behaves differently for ElectricCar and SportsCar.

  5. Abstraction

    • Focus on essential features, hiding unnecessary details.

    • Achieved using abstract classes or interfaces.

    • Example: interface Vehicle { drive(); } → implemented by Car, Bike, etc.

Benefits of OOD

  • Modularity – System is divided into manageable objects.

  • Reusability – Classes can be reused across projects.

  • Maintainability – Changes in one class have minimal impact on others.

  • Scalability – Easy to extend system with new classes.

  • Real-world Modeling – Mirrors real-world entities, making design intuitive.

Example in Real Life

  • Class: Employee

  • Attributes: name, id, salary

  • Methods: calculateSalary(), promote()

  • Inheritance: Manager and Developer inherit from Employee

  • Polymorphism: calculateSalary() works differently for Manager and Developer.