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.