2110

Question 1

Does an abstract class need to be instantiated?

Answer 1

No - it just defines variables t methods these methods can
Also be abstract

Question 2

Do subclasses of an abstract class need to inherit variables & methods of their superclass?

Answer 2

Yes

Question 3

Which class type i just a header and no body?

Answer 3

An abstract class

Question 4

Abstract class syntax

Question 5

What is an interface

Answer 5

Just a collection of method declaration • no data no body

Question 6

How does a class implement an interface

Answer 6

It guarantees to use all the methods! Therefore an interface enforces an API in software design

Question 7

Interface syntax

Question 8

How is java  Standard library organized?

Answer 8

In one large class hierarchy where the object class is the parent of all classes. every single class implicitly extends the object class

Question 9

Three pillars of object oriented programs

Answer 9

Encapsulation, inheritance and polymorphism

Question 10

Define encapsulation

Question 11

Define iwhentance

Question 12

Define polymorphism

Answer 12

The ability Of one object to be treated, used like another this works for objects in the inheritance hierarchy

Question 13

Can me use a reference of a superclass type to refer to an object of its subclass type

Answer 13

Yes

Question 14

What allows us to place objects from different steps within a class hierarchy into the same array?

Answer 14

Polymorphism

Question 15

Does polymorphism work bottom up in a class hierarchy?

Answer 15

No! Only top down

Question 16

What is the instanceOf operator?

Answer 16

Used to keep track of what type of object is being referred to by a variable

. X instanceof Y returns true if X refers to an object of type Y or a subclass (any number of levels down) of Y.

Question 17

What is casting? In the context of class hierarchy

Answer 17

Changing the type Of a variable (can be risky bc precision loss)

In the context of a class hierarchy it only works downwards

Question 18

Can casting be done in reverse? Can we use the reference of a subclass type to refer to an object of a superclass type

Answer 18

Yes but also risky

Question 19

Encapsulation

Answer 19

Defining objects (this is done within class files)

Question 20

The two main components of an object

Answer 20

Variable declaration and methods

Question 21

Mutator / accessor methods

Answer 21

Setters & getters

Question 22

This keyword

Answer 22

Used to distinguish the instance variable from the method parameter

Question 23

In method overloading WHAT needs to be different it the name is the same?

Answer 23

Its signature (this means types order of its input parameters)

Question 24

Can constructors be overloaded?

Answer 24

Yes

Question 25

Static methods

Answer 25

Can be used not on an object

className.staticMethodName(parameters);

The class name can be ignored if its called from the class

All methods used in procedural programming are static

Question 26

Instance variables

Answer 26

Each object gets its version of this variable