OOP

Question 1

What Is OOP

Answer 1

a type of computer programming (software design) in which programmers define not only the data type of a data structure, but also the types
of operations (functions) that can be applied to the data structure.
In this way, the data structure becomes an object that includes both data and functions. In addition, programmers can create relationships between one object and another. For example,
objects can inherit characteristics from other objects.

Question 2

What are the advantages of OOP

Answer 2

-Code Reuse
-Encapsulation
-Design benefits as easier to program due to extensive planning phase at beginning
-Software maintenance is easy

Question 3

What is encapsulation

Answer 3

a programming language construct that facilitates the bundling of data with the
methods (or other functions) operating on that data.
Encapsulation is an OOP concept where object state(class fields) and it’s behavior(methods) is
wrapped together. Java provides encapsulation using class.

Question 4

What are the benefits of encapsulation

Answer 4

-you can use a method without knowing how it works. Once an
Object is created
-hide certain parts of themselves from
programmers. This prevents progrmers from tampering with values they
shouldn’t.
-object controls how one interacts with it, preventing
other kinds of errors.

Question 5

What is a class

Answer 5

a construct that is used to define a distinct new type and is made up of
properties (attributes) that are grouped together to describe the object and
functions and procedures (methods/behaviour) that describes what the object can do.

Question 6

What other words can be used to describe a class

Answer 6

-a building plan for a house
-a template
-a blueprint

Question 7

What does the first part of a UML diagram show

Answer 7

properties/ fields of class with their data types – describe what object “looks
like”

Question 8

What does the second part of a UML diagram show

Answer 8

methods

Question 9

What does the + access modifier mean

Answer 9

accessible from outside class in any other class

Question 10

What does the - access modifier mean

Answer 10

NOT accessible from outside class

Question 11

What does the access modifier protected mean

Answer 11

only accesible in child class that inherits from parent class.

Question 12

What is an object

Answer 12

a dynamic instance of a class.

Question 13

How is an object instantiated

Answer 13

Using the constructor

Question 14

What is a constructor

Answer 14

code in a special method that
will create the object in memory while the program is running.

Question 15

What a the relationship between objects and classes

Answer 15

Many objects can be created
from the same class. Just like you can declare many variables of the same type, you can have
many instances of your class as objects in one application Each object can have its own values

Question 16

What is information hiding

Answer 16

a programming language mechanism for restricting access to some of the
object’s components. When fields and methods are declared under private in the class, it is only
visible in the object itself. These private variables and methods are protected against
unintentional modification.

Question 17

How can you access private variables

Answer 17

by using typed methods to
get the values and make it available to the unit where the object is used.(getters)

Question 18

How do you change private variables

Answer 18

by using void methods to
set values.(setters)

Question 19

What are the constructor, accessor and mutator methods set as

Answer 19

The Constructor, Accessor methods and Mutator methods must be declared as public so
that other units can use them.

Question 20

How do you determine the name of a constructor

Answer 20

The name of a constructor must be the same name as the class

Question 21

Is it possible to have more than one constructor

Answer 21

Yes !
Like a no argument constructor which is the default constructor etc

Question 22

What is an argument list

Answer 22

The parameters of the constructor (The variables in the brackets next to the constructor )

Question 23

What are the two types of constructors

Answer 23

Parameterised constructor and default constructor

Question 24

What is a parameterised constructor

Answer 24

You can provide your constructor with parameters to
initialise fields to values of your choice each time the constructor is called

Question 25

What is a default constructor

Answer 25

The default constructor uses the inherited create constructor to set
the strings to empty fields and numeric values to 0 if it is not defined, but you can code
the default constructor to set initial values

Question 26

What is overloading

Answer 26

When a class have two methods with the same name, with different parameters
(Ie define two constructors using the same name, with different parameters)

Question 27

What are the characteristics of accessor methods (getters)

Answer 27

always typed method
always brackets
always returns a value

Question 28

What is an accessor method

Answer 28

a typed method in the class that makes private variables in the class
available to the driver class or any other unit.

Question 29

What is a driver program

Answer 29

A class with a form

Question 30

How would you call an accessor method in the driver class

Answer 30

object.methodname()

Question 31

What are the characteristics of mutator methods (setters)

Answer 31

always void method
Sometimes a parameter in brackets with new value
no return statement

Question 32

What is a mutator method

Answer 32

a procedure to change or set the private variables in the object after the
object was instantiated. You make use of mutators to transfer the new values to the private
variables.

Question 33

How would you call a mutator method in the driver class

Answer 33

object.methodname(changed value)

Question 34

What is an auxiliary method

Answer 34

any other methods in the class that can assist with calculation or
formatting.

Question 35

What is inheritance

Answer 35

mechanism of creating new classes build upon existing ones in which one object takes on all fields and methods of the
parent object.

Question 36

What does the object class do

Answer 36

The Object class, defined in the java.lang package, defines and implements behavior common to
all classes—including the ones that you write.

Question 37

What is the keyword in inheritance

Answer 37

Super

Question 38

How to check it an object is an instance of a particular class

Answer 38

Use instanceof

Question 39

What type of members can a subclass inherit from its parent class

Answer 39

A subclass does not inherit the private members of its parent class. However, if the superclass has public or protected (other classes cannot use these variables but child classes can) methods for accessing its private fields, these can also be used by the
subclass.

Question 40

How to override the superclass

Answer 40

You can write a new instance method in the subclass that has the same signature as the
one in the superclass, thus overriding it

Question 41

How to hide the super class

Answer 41

You can write a new static method in the subclass that has the same signature as the one
in the superclass, thus hiding it.

Question 42

What is overriding

Answer 42

when the child class has a method of the same name and parameters as the parents
thus hiding the parent’s method