Object-Oriented Hierarchies

Types of Hierarchies

1. Has-a / Part-of (Association/Containment)
   • Represents component relationships
   • Example: Car has-a Engine
2. Is-a / Kind-of (Inheritance/Generalization)
   • Represents type relationships
   • Example: Employee is-a Person
3. Use-a (Dependency)
   • When one class uses another class but doesn't own it
   • Example: Class A uses Class B as a method parameter
4. Creates-a (Instantiation)
   • When one class creates instances of another class
   • Common in factory design patterns

Association (Has-a Relationship)

• When an object is part of or component of another object
• Implemented by declaring an object of one class as a data member in another class

class Engine {};
class Car {
private:
    Engine e; // Association
};

Types of Association

1. Composition (Strong Association)
   • Dependency object cannot exist without the dependent object
   • Represents tight coupling
   • Example: Heart cannot exist without the Human
2. Aggregation (Weak Association)
   • Dependency object can exist without the dependent object
   • Represents loose coupling
   • Example: Department and Faculty

Inheritance (Is-a Relationship)

• When one class is a specialized version of another class
• Syntax: class Derived : [mode] Base {}
• Base class is an abstraction for the derived class

What Gets Inherited

• All data members (private/protected/public, static/non-static)
• Only non-static data members get space in the object