Quiz 5: Inheritance 1

1. Which is relevant to the concept of inheritance in object-oriented programming?

  • Dynamic Binding
  • Method Overriding
  • Polymorphism
  • All of them

Correct answer: All of them

Explanation:

  • Polymorphism: a child class can "stand in" for its parent class.
  • Method Overriding: child class overrides a method inherited from a parent class
  • Dynamic Binding: more complicated - see the information under the dynamic binding definition in section 5.3

More information can be found in Section 5.3.

2. In the Square vs. Rectangle example discussed in class, which statement is correct?

  • Rectangle should be a subclass of Square
  • There should be no inheritance relationship between Rectangle and Square
  • Square should be a subclass of Rectangle
  • Either Rectangle or Square should be a subclass of the other

Correct answer: There should be no inheritance relationship between Rectangle and Square

Explanation:

In a mathematical sense, every square is a rectangle.

However, if a Square were to inherit from a Rectangle, it would inherit methods such as setWidth() and setHeight(). The Square could override these functions to provide correct functionality, but publicly exposing such an API defies the fundamental property of a square: a rectangle with equal height and width.

This is fundamentally the same issue as the Stack<E> extends Vector<E> problem.

Further reading (consider the subtype definition)

3. Which of the following views about inheritance is based on the "is-a" relation?

  • Neither type view nor module view
  • Type view
  • Module view
  • Both type and module views

Correct answer: Type View

Explanation:

Recall the definition for subtype:

Data type \(t_2\) is a subtype of data type \(t_1\) if every value of \(t_2\) can be assigned to a variable of \(t_1\).

4. In Java, Stack is a subclass of Vector. Which of the following statements is incorrect?

  • The LIFO property of Stack can be violated when the methods inherited from Vector are called.
  • Stack reflects the module view of inheritance for code reuse.
  • Stack reflects the type view of inheritance.
  • Stack inherits all the methods of Vector.

Correct answer: Stack reflects the type view of inheritance.

Explanation:

The statement is incorrect because a Stack is not a Vector. The essential quality of a Stack is its LIFO property, which is violated by several methods inherited from Vector.