Object Oriented Programming - Java

Question 1

The . Operator

Answer 1

The . operator gives you access to all members of a given class. Including access to the variables that the object holds

Question 2

What is a class?

Answer 2

A class is a user-defined blueprint from where objects are created

Question 3

What are members of a class?

Answer 3

Members of a class are all of its fields, properties, methods, and everything that defines it

Question 4

How do you create a Class?

Answer 4

• Define Properties
• Give values to the Properties
• Create an Instance of the Object(class)

Question 5

What is a namespace?

Answer 5

The namespace lets you organize your classes and files. The class name should match the name of the .cs file and the namespace name should match the name of the folder the .cs file is in.

• add ( using FileName; ) at the top of .cs file to import a class from another folder.
• namespaces can have subnamespaces

Question 6

Define Constructors

Answer 6

Constructor is the method that constructs your class.
It has the name of the class and no data type and it may or may not take in arguments.

Question 7

Explain the line of code: "Point point = new Point();"
     class Point
    {
        public int x;
        public int y;
    } 

     class EntryPoint
    {
        static void Main()
        {
            Point point = new Point();
            point.x = 5;
            point.y = 3;
            Console.WriteLine(point.x);
            Console.WriteLine(point.y);
        }
    }

Answer 7

• we created a new variable with a data type, Point

- new Point(), is a new object with data type, Point

Question 8

Explain what the new keyword means below:
     class Point
    {
        public int x;
        public int y;
    } 

     class EntryPoint
    {
        static void Main()
        {
            Point point = new Point();
            point.x = 5;
            point.y = 3;
            Console.WriteLine(point.x);
            Console.WriteLine(point.y);
        }
    }

Answer 8

• When you use the new keyword you are creating a new instance of the given class(object), this is called instantiation

Question 9

Explain what the “this” keyword does for a class

Answer 9

this, keyword gives you access to members of your class and lets you distinguish between two variables that have the same name.
- Use the this keyword to show that you are referencing a member from your class if there is a variable naming conflict.

Question 10

What is the protection level on a field and how do you access them?

Answer 10

Fields are almost always private, they are not directly exposed to the “outside world”. Their values can be accessed only by a Property or some other logic in your Class.

Question 11

What is the purpose of using a get and set inside of a property instead of just making a field public?

Answer 11

• You can implement validation logic inside the scopes of get and set. Ex, you may want to set the value to x only if its between 5 and 10.
• Between the get and set { } you can perform validation using if statements or loops

Question 12

explain get{ }

Answer 12

get returns the value of the field that we are using or referencing inside of the property

Question 13

explain set{ }

Answer 13

sets the value, meaning for example it sets or gives the value of the x property to the x field

Question 14

What do different versions of get and set control?

Answer 14

• we can control if a given Property is Read-Only, Write-Only or Read-Write.

Question 15

What is a getter and setter in read-only and write-only terms?

Answer 15

Getter = Read
Setter = Write

Question 16

How to access static fields?

Answer 16

Static Fields(Static Members in general) are not dependant on the instance of a given class. They can be accessed directly from the class without instantiating it.

Question 17

What is the value of the static field dependent on?

Answer 17

The value of a Static Field is NOT dependent on a Class instance. The static field is “shared” amongst all instances of the Class and they all can modify or access it internally.

Question 18

How can static fields be shared?

Answer 18

• You can use a public static field to share a variable between all instances of your class.
• Each class can access and change the variable of that field.

Question 19

What are the two different kinds of constants?

Answer 19

1. const keyword
2. readonly keyword

Note. Constants are written in all Caps and separated with an underscore. ex.1) ID ex.2) THE_NAME_OF_THE_CONST

Question 20

What is the const keyword? How do you access the field with this constant?

Answer 20

const = value hardcoded in the code.

• when creating the const you have to assign the value to the const.
• • const constants are static by default. This means they are accessed the same as static fields through the class. ex.) User.HEIGHT;

Question 21

What is the readonly keyword? How do you access the field with this constant?

Answer 21

readonly = value assigned later on in code logic

• get their value from inside of the constructor
• the readonly is accessed through the variable assigned to the new object()

Question 22

Why do constants exist for fields?

Answer 22

We should not be able to directly modify any public fields after instantiating a class.
- Constants of any kind can not change their value once it is set

Question 23

What is Enumeration?

Answer 23

Enumeration is used to prevent possible mistakes by a User, by giving them a set of values from which they can choose from.

Question 24

Can static classes have constructors?

Answer 24

No, Static classes can not have constructors as they can NOT be instantiated so they do not need one.

Question 25

Public - what is it in the main method?

Answer 25

Public is an access modifier. An access modifier determines the accessibility of the class, variable, or method.

Question 26

name the eight primitive data types in Java

Answer 26

boolean, byte, char, short, int, long, float, double

Question 27

Method Overloading

Answer 27

It is the ability to create more than one method with the same name, as long as it has different parameters.

Question 28

public/private static final

Answer 28

this is how to create a constant value in Java. The final keyword determines if the variable is a constant

Question 29

Java switch statement

Answer 29

Can only be used with byte, short, char and int data types