Polymorphism

Question 1

Describe a monomorphic language

Answer 1

A language in which every value and variable can only be interpreted to be of one type

Question 2

Define polymorphism

Answer 2

Some values and variables may have more than one type

Question 3

What are the two categories for polymorphism?

Answer 3

Ad hoc

Universal

Question 4

What are the four types of polymorphism?

Answer 4

Overloading
Coercion
Inclusion
Parametric

Question 5

What are the two types of ad hoc polymorphism?

Answer 5

Overloading

Coercion

Question 6

What are the two types of universal polymorphism?

Answer 6

Inclusion

Parametric

Question 7

State some advantages of polymorphism

Answer 7

• allows method to perform similar tasks accessed under a common name
• allows you to define multiple constructors
• less repetition of code

Question 8

Describe overloading polymorphism

Answer 8

Same function name is used to denote different types, operator can be applied to operands of different types
i.e.
2 + 3, “hello” + “world”

Question 9

Describe coercion polymorphism

Answer 9

This is where an instance of one type is forced to be interpreted as another
e.g. if operator + could only add real numbers, integer types converted before operator applied

Question 10

What does it mean for an object to be a subtype of another?

Answer 10

One type is a sub type of another if it related by extends or implements cause

Question 11

What is another name for inclusion polymorphism?

Answer 11

Subtype polymorphism

Question 12

Describe inclusion polymorphism

Answer 12

Instance of a subtype can be manipulated as if it was an instance of the supertype

Question 13

Describe late binding

Answer 13

When a method call is made, dynamically select the version of the method that is used
Don’t know statically what will happen

Question 14

Describe parametric polymorphism

Answer 14

The code features an implicit or explicit type parameter
Can be used for value of any suitable type
The code does not depend on the value given at run time

Question 15

Define recursion

Answer 15

Process in which a problem is defined in terms of itself. The problem is solved by repeatedly breaking it into smaller problems which are similar in nature to the original problem.

Question 16

Advantages of recursion

Answer 16

• reduces the length of the code
• useful for dealing with inherently recursive structures, such as trees and graphs
• makes the code more readable

Question 17

State some inefficiencies of recursion

Answer 17

• excessive memory requirements (memory required by Java to keep track of all the recursive calls)
• excessive re-computation

Question 18

What does it mean for a function to be tail recursive?

Answer 18

When the recursive call is the last thing executed by the function

Question 19

How does tail call optimisation work?

Answer 19

Since the recursive call is the last statement, there is nothing less to do in the current function, so saving the current function’s stack frame is pointless and it can be disregarded