a) Inheritance, Composition, and Aggregation in OOAD (6 Marks)
1. Inheritance
Definition: A mechanism where one class (child/subclass) derives properties and behavior from
another class (parent/superclass).
Example:
class Animal {
void eat() { System.out.println("This animal eats."); }
}
class Dog extends Animal {
void bark() { System.out.println("Dog barks."); }
}
Explanation: Dog inherits eat() from Animal.
2. Composition
Definition: A “has-a” relationship where one class contains an instance of another class. It
implies strong ownership; if the container is destroyed, so is the contained object.
Example:
class Engine {
void start() { System.out.println("Engine starts"); }
}
class Car {
private Engine engine = new Engine();
}
Explanation: Car has-a Engine. If Car is destroyed, so is the Engine.
3. Aggregation
Definition: A weaker “has-a” relationship compared to composition. The contained object can
exist independently of the container.
Example:
class Teacher {
String name;
}
class Department {
List<Teacher> teachers;
}
