Topic 4 - Inheritance

Question 1

Define: inheritance

Answer 1

a mechanism for deriving a new class from an existing one

Question 2

Motivation for inheritance?

Answer 2

• can reuse existing classes

- can organize classes in hierarchical manner - can go from more general to more specific classes

Question 3

Inheritance Terminology: The derived new class is called the _______?

Answer 3

subclass; child class; derived class

Question 4

What does the subclass inherit?

Answer 4

Inherits the parent class or base class

Question 5

Define: protected.

Answer 5

Class=Y | Package = Y | Subclass = Y | Subclasses in other packages = Y | Any class in other packages = N

Question 6

Define: polymorphism

Answer 6

the principle that behaviour can vary, depending on the type of the object being manipulated. With inheritance, a variable can refer to objects of different types during it lifetime

Question 7

Overriding methods: which method is actually executed at runtime?

Answer 7

Depends on which object is used to invoke the method

Question 8

Type of an object = when is it determined and when can it change?

Answer 8

Type of an object is determined when it is created and cannot change - note that we are not talking about the type of a VARIABLE here

Question 9

When invoking toString() on an object, what determines what is printed and what does not determine what’s printed?

Answer 9

What’s printed depends on the actual type of the object (not the type of the variable)

Question 10

What does dynamic binding or late binding of the variable to the type of the object mean?

Answer 10

It is not known which method should be invoked until run time

Question 11

Read the following: 
public void deposit(double amount){ 
transactionCount++;
super.deposit(amount);
}
What would happen if we did not have the super reference here?

Answer 11

It would enter an infinite loop.

Question 12

Can a class inherit from two classes the same time? (multiple inheritance)

Answer 12

You cannot have multiple inheritance.
You can have "class extends A
implements B" because B is an interface, not a class so does not violate rule of multiple inheritance,

Question 13

“instanceof” is a?

Answer 13

An operator.