Object Oriented Programming

Question 1

Constructor vs. Method Facts:

Constructor

Answer 1

1. A constructor is used to initialize the state of an object.
2. A constructor must not have a return type.
3. the constructor is invoked implicitly.
4. The Java compiler provides a default constructor if you don’t have any constructor in a class.
5. the constructor name must be the same as the class name.

Question 2

Describe object-oriented programming?

Answer 2

A methodology or paradigm to design a program using classes and objects.

It includes concepts such as: Object, Classes, Inheritance, Polymorphism, Abstraction, Encapsulation

Question 3

One of the 4 pillar of OOP is Encapsulation. What is Encapsulation ?

Answer 3

Encapsulation is a process of wrapping code and data together into a single unit

We can encapsulate an entire class by making all the data members of the class private (data hiding). We can use the getter and setter methods.

Question 4

What is a parameterized Constructor ?

Answer 4

A parameterized constructor is one that has a specific number of parameters. It’s used to provide different values to the distinct objects.

Question 5

What is Constructor Overloading ?

Answer 5

Constructor overloading is when there are more than one constructor with different parameter lists. Each constructor performs a different task. They are differentiated by the number of parameters in the list and their list types.

Question 6

What is the default constructor ?

Answer 6

The default constructor is a no-args constructor that the Java compiler inserts automatically. It contains a default call to super()

Question 7

What is method overloading ?

Answer 7

Method overloading is when a class has multiple methods of the same name, but different in parameters.

A method can be overloaded by :

1. changing number of arguments
2. changing the data type

This is a compile time polymorphism

Question 8

What is an abstract method ?

Answer 8

A method that is declared as abstract and does not have implementation

Question 9

What are some advantages of inheritance ?

Answer 9

1. Method Overriding

2. Code Reusability

Question 10

What is the extends keyword ?

Answer 10

The extends keyword indicates that you are making a new class that derives from an existing class.

Question 11

What are the 2 types of constructors ?

Answer 11

Default and Parameterized

Question 12

Constructor vs. Method Facts:

Method

Answer 12

1. A method is used to expose the behavior of an object.
2. A method must have a return type.
3. The method is invoked explicitly.
4. The method is not provided by the compiler in any case.
5. The method name may or may not be the same as class name.

Question 13

When is a constructor called ?

Answer 13

A constructor is called when an object is created.

Question 14

What is generalization (abstraction)

Answer 14

Generalization is the process of extracting shared characteristics from two or more classes, and combining them into a generalized superclass.

Question 15

What is an object?

Answer 15

Any entity that has state and behavior. It can be defined as an instance of a class.

Ex. chair, pen, table, keyboard

Question 16

What is method overriding ?

Answer 16

Method overriding is when a subclass has the same method as declared in the parent class

1. Used to provided the specific implementation of a method which is already provided by its superclass.
2. A static method cannot be overridden.
3. Runtime polymorphism

Question 17

What are some advantages of OOP over Procedural Oriented Programming?

Answer 17

1. OOP makes development and maintenance easier as project size increases.
2. OOP provides data hiding

Question 18

What is a constructor ?

Answer 18

A constructor is called when an instance of the object is created, and memory is allocated for the object. Used to initialize the object

Question 19

What are the 3 types of inheritance in java ?

Answer 19

single, multilevel, and hierarchical

Question 20

What is an abstract class ?

Answer 20

An abstract class is one that is declared as abstract. It needs to be extended and its method implemented. It cannot be instantiated.

Question 21

One of the four pillars of OOP is Inheritance. Describe Inheritance.

Answer 21

Inheritance is a mechanism in which one object acquires all of the properties and behaviors of a parent object.

The idea behind it is that you can create new classes that are built upon existing classes. When inheriting, you can reuse methods and fields of the parent class and also add new ones.

It represents the IS-A relationship which is known as a parent-child relationship

Question 22

What is Sub Class/Child Class ?

Answer 22

Subclass is a class which inherits the other class. It is also called the derived classes, extended class, or child class

Question 23

What are the 2 ways to achieve abstraction ?

Answer 23

1. Abstract class

2. Interface

Question 24

One of the 4 pillars of OOP is Abstraction. Define Abstraction.

Answer 24

Abstraction is a process of hiding the implementation details and showing only functionality to the user. It focuses on what the object does and not how it does it.

Question 25

What is Specialization ?

Answer 25

Specialization means creating new subclasses from an existing class. It certain attributes, associations, or methods only apply to some of the objects of the class, a subclass can be created.

Question 26

What is a class?

Answer 26

A class is a “blueprint from which individual objects are created”. It’s a template that is used to create objects, and to define object data types and methods that may be used by the object.

Question 27

What is a Super class/Parent class

Answer 27

A Superclass is the class from where a subclass inherits the features. It is also called a base class or parent class.

Question 28

One of the four pillars of OOP is Polymorphism. Describe Polymorphism

Answer 28

Polymorphism is the ability of an object to take on many forms. It allows us to perform a single action in many ways.

It occurs when a parent class reference is used to refer to a child class object.