Unit_7: Form of Inheritance, Substitution

Question 1

What are 9 forms of Inheritance?

Answer 1

1. Specialization: subclass is a specialized form
2. Specification: parent describes required behavior (abstract)
3. Construction: subclass constructs something different
4. Generalization: subclass is a more general object
5. Extension: subclass adds new methods, but no overriding
6. Limitation: removal of functionality in the subclass
7. Containment: use another class as instance variable
8. Variance: forcing parent-child relationship instead of creating abstract class on top
9. Combination: when using multiple inheritance
   No substitution (No Is-a relationship): 3,4,6,8

Question 2

What type of inheritance is this? Is it
a good or bad form of inheritance?
Java
class Node{…}
class MyList{
private Node first;
public Node getFirst(){
return first;
}
}

Answer 2

Type: ✅ Composition (not inheritance)

MyList has a Node — this is called composition (a “has-a” relationship).

There is no extends keyword, so MyList does not inherit from Node.

=> good design! OO prefer composition: more modular, flexible

Question 3

What type of inheritance is this? Is it
a good or bad form of inheritance?
Java
class Car{
private int age;
public int getAge(){return age;}
public void setAge(int a){age = a;}
public void startCar(){…code to start the car…}
}
class EnginelessCar extends Car{
public void startCar(){}
}

Answer 3

specialization
Bad: Violates Liskov Substitution Principle — EnginelessCar shouldn’t inherit behavior it can’t support.

Fix: Refactor using composition or better class hierarchy (e.g., both inherit from a general Vehicle class).

Question 4

What type of inheritance is this? Is it
a good or bad form of inheritance?
C++
class Adult{…};
class Student{…};
class GradStudent : public Adult, public Student{…}

Answer 4

Type: Combination

Good/Bad: ⚠️ Potentially bad – can cause ambiguity (e.g., if both Adult and Student define the same method like getID())

Use carefully with virtual inheritance to avoid the diamond problem

Question 5

What type of inheritance is this? Is it
a good or bad form of inheritance?
Java
class Bear{
public void eat(){…}
public void sleep(){…}
}
class Person extends Bear{
public void cook(){…}
}

Answer 5

Type: Specialization
Bad design: A Person is not a type of Bear, so using inheritance here creates a misleading “is-a” relationship.
Better approach: Use composition (containment) instead, where a Person could have a Bear as a member.

Question 6

What type of inheritance is this? Is it
a good or bad form of inheritance?
Java
abstract class 2DShape{
public abstract double calculateArea();
}
class Circle extends 2DShape{
…
}

Answer 6

Type: Specification

Good: 2DShape describes a required behavior (abstract method calculateArea()), and Circle specifies the behavior for that shape. it uses inheritance to ensure that all shapes (like Circle) will have a method to calculate area.

Question 7

What type of inheritance is this?
How would you reorganize?
Java
class Tiger{…}
class Lion extends Tiger{…}

Answer 7

Type: Specialization :Lion is a specialized form of Tiger. It represents a more specific type of Tiger.

Reorganize as a more general class:
Since Lion and Tiger are both types of big cats, it might make sense to introduce a more general BigCat class, with shared properties and methods, and then have Lion and Tiger inherit from it.

Question 8

What type of inheritance is this Is it a
good or bad form of inheritance?
Java
class Feline{…}
class Lion extends Feline{…}

Answer 8

Specialization: Lion is a specialized form of Feline. A Lion is a specific type of Feline, and it inherits properties and behaviors from the Feline class.

Good form of inheritance (in this case)