Week 6

Question 1

A general relationship that describes an activity between 2 classes

Answer 1

Association

Question 2

How are associations denoted? How do the 2 classes relate?

Answer 2

A straight line arrow and direction. They relate through their objects.

Question 3

To communicate between each other, 2 classes must have a link between them. What is this link represented by?

Answer 3

Association.

Question 4

What are 2 form of association?

Answer 4

Aggregation and composition

Question 5

A relationship where an objects owns a collection of other identical objects

Answer 5

Aggregation, also known as a has-a relationship

Question 6

What are some examples of aggregations?

Answer 6

Professor has many students, hotel has many suites. One way, reverse not possible

Question 7

T/F - An aggregation relationship is represented by a field in the aggregating class

Answer 7

True

Aggregated class
public class Name {}

Aggregating class
public class Student {
private Name name;
private Address address;
…
}

Question 8

Relationship where a class contains other references to other classes

Answer 8

Composition (has-a relationship)

IE. Room has a door, Car has a wheel

Question 9

T/F - Composition is a special cast of aggregation

Answer 9

True

Question 10

In __________ a child can exist independently of the parent, in ___________ the child cannot exist independent of the parent

Answer 10

Aggregation, composition

Question 11

Composition vs Aggregation, types of association

Answer 11

Composition: Strong association
Aggregation: Weak association

Question 12

Inheritance has what type of relationship?

Answer 12

is-a relationship

Question 13

the ___class is a specialization of the _____class, and has characteristics of it

Answer 13

subclass, superclass

Question 14

Can a subclass be treated like a parent type?

Answer 14

Yes. A motorcycle is-a vehicle. A car is-a vehicle.

Question 15

Can every class be inherited?

Answer 15

No, final classes cannot.

Question 16

Can a class inherit from more than one class ?

Answer 16

No, Java does not support multiple inheritance

Question 17

What rules are there pertaining to the super keyword?

Answer 17

Super() can only be used inside the subclass constructor and it must be the first statement.

Question 18

Can any other method in the subclass call the superclass constructor? (super())

Answer 18

No

Question 19

Do we always need to call the superclass constructor when we instantiate a subclass object? Why?

Answer 19

Yes. When a subclass object is instantiated the subclass object must also automatically execute one of the constructors of the superclass.

Otherwise you wouldn’t be able to inherit anything.

Question 20

How do you prevent a method in a class from being overridden in a subclass?

Answer 20

There’s a number of ways.
1. Use a static method
2. Make a private access modifier
3. You can prevent a method being overridden by subclasses by declaring it as final.

Something about default modifiers but that’s eh

Question 21

Overload vs override

Answer 21

1.
Override = methods of same name and signature
Overload = methods of same name, different signature

2. Chaining can be achieved using the “this” keyword, while subclasses may call super classes using the “super” keyword
3. Constuctors can be overloaded, but constructors cannot be inherited.

Question 22

Overloading occurs at _______-time, while overriding occurs at ___-___

Answer 22

compile time, run time

Question 23

What does compile time denote? What does run time denote? How does the former relate to static?

Answer 23

Compile time denotes the time of program
compilation, Run-time denotes the time of program
execution

Static refers to anything created at compile time, and remains