To understand the differences between has-a and is-a relationships, let's first define them:
- Has-a relationship: This is a composition relationship between two classes where one class contains an instance of the other class as a member variable. It represents a "part-of" relationship.
- Is-a relationship: This is an inheritance relationship between two classes where one class is a subclass of the other class. It represents a "kind-of" relationship.
Now, let's go through each option to understand why it is correct or incorrect:
Option A) Inheritance represents an is-a relationship - This option is true because inheritance is used to create a subclass that is a specialized version of the superclass. The subclass "is-a" kind of the superclass.
Option B) Inheritance represents a has-a relationship - This option is incorrect because inheritance does not involve composition between two classes. It is used to create a specialized version of an existing class.
Option C) Interfaces must be used when creating a has-a relationship - This option is incorrect because interfaces are not required to create a has-a relationship. A has-a relationship can be created using instance variables.
Option D) Instance variables can be used when creating a has-a relationship - This option is true because instance variables can be used to represent the composition relationship between two classes. One class can contain an instance of the other class as a member variable.
Therefore, the correct options are A and D.