Unit_2

Question 1

When to use abstract class over in interface?

Answer 1

1. Use Abstract Class when:
   - Classes share common code
   - Need to maintain state
   - Want to provide a base implementation
   - Classes are closely related
2. Use Interface when:
   - Only defining behavior
   - Need multiple inheritance
   - Want to define a contract
   - Classes are unrelated but share behavior

Question 2

What is inherit? when to use extend?

Answer 2

hierarchies of classes and subclasses => “is-a” relationship, we use extends

Question 3

What is containment?

Answer 3

Containment relationship:
* when an object contains an instance of another as
one of its data members (instance variables)
=> “has-a” relationship, eg Book has an author.

Question 4

When does abstract class need constructor?

Answer 4

Nothing to initialize unless it declare data members for inheritance purpose)

Question 5

Why you can never create an instance of an abstract class?

Answer 5

because abstract class is template/blueprint -> contains incomplete methods, and design to be inherited from, not used directly.

But you can define >= 1 constructors

Question 6

What is golden rule in Abstract class/method

Answer 6

1. if you define data, other than public constants, you tell people how the’re allowed to use it. you DON’T let them use it directly

Question 7

What is LSP?

Answer 7

if Child is a subclass of Parent -> instance of Parent can be substituted by instances of Child