Week 8 - OOP - Object Oriented Programming Principles and Intermediate Java

Question 1

4 pillars of OOP

Answer 1

Abstraction
Inheritence
Polymorphisim
Encapsulation

Question 2

What is inheritance?

Answer 2

Inheritance is all about inheriting the common state and behavior of parent class (super class) by its derived class (sub class or child class). A sub class can inherit all non-private members from super class, by default.

Question 3

Inheritance can be one of four types – depending on classes hierarchy. Name them:

Answer 3

Single inheritance
Multi-level inheritance
Hierarchical inheritance
Multiple inheritance

Question 4

What is Single inheritance

Answer 4

There is one Parent class and one Child class. One child class extends one parent class

Question 5

Multi-level inheritance

Answer 5

In multilevel inheritance, there will be inheritance between more than three classes in such a way that a child class will act as parent class for another child class.

Question 6

Hierarchical inheritance

Answer 6

In hierarchical inheritance, there is one super class and more than one sub classes extend the super class.

Question 7

Multiple inheritance

Answer 7

In multiple inheritance, a class can inherit the behavior from more than one parent classes as well.

Question 8

____ is a type of inheritance where there is one Parent class and one Child class. One child class extends one parent class.

Answer 8

Single inheritance

Question 9

____ is a type of inheritance where there is one super class and more than one sub class extend the super class.

Answer 9

Hierarcihal inheritance

Question 10

What is an object class?

Answer 10

a special class in Java which is the root class from which all other classes inherit, either directly or indirectly.

Question 11

The _____ method returns a copy of this object.

Answer 11

clone

Question 12

The _____ method returns a Class object that represents this object’s runtime class

Answer 12

getClass

Question 13

The _____ method returns a String representation of this object.

Answer 13

toString

Question 14

In java equals() method is used to compare equality of

Answer 14

two Objects

Question 15

_____ is the default implementation of the equals() method which only checks if two object references refer to the same object.

Answer 15

Shallow comparison

Question 16

_____ is where data members of objects are to be compared with one another.

Answer 16

Deep comparison

Question 17

During the execution of the application, if hashCode() is invoked more than once on the same object then it must consistently return the same Integer value. T/F

Answer 17

True

Question 18

Different executions of the same application using hashcode() must produce the same integer every time. T/F?

Answer 18

False

Question 19

What is polymorphism?

Answer 19

“taking on many forms”. In the realm of programming, it describes how objects can behave differently in different contexts. The most common examples of polymorphism are method overloading and overriding.

Question 20

What is method overloading ?

Answer 20

is when there exist two or more methods in a class with the same method name, but different method signatures by changing the parameter list.

Question 21

What is method overriding>

Answer 21

is when a method in a child class has the same method signature as a method in the parent class, but with a different implementation. Thus, child classes can change the default behavior given by a parent’s method. Overriding methods makes class hierarchies more flexible and dynamic.

Question 22

What does object-oriented programming mean?

Answer 22

Programming constructs are objects which model real-world concepts and can be put into hierarchies, and the relationship between objects are managed

Question 23

What is the difference between classes and objects?

Answer 23

Classes are the templates from which objects are instantiated

Question 24

What does polymorphism mean?

Answer 24

Allowing the implementation of a given behavior to vary, whether between subclasses or within the same class

Question 25

What are generics?

Answer 25

constructs introduced in Java 5 which enforce compile time safety by allowing you to use parameterized types.

Question 26

Generics can be declared on a

Answer 26

class (generic types), method parameters (generic methods), or return types.

Question 27

With generics, you can restrict a class to only

Answer 27

accept objects of a given type and the compiler will prevent you from using any other type.

Question 28

_____ are constructs introduced in Java which enforce compile time safety by allowing you to use parameterized types.

Answer 28

Generics

Question 29

To make a class (or interface) generic, use _____ when declaring it

Answer 29

angle brackets

Question 30

what is abstraction?

Answer 30

It involves identifying common characteristics and generalizing behaviors into conceptual classes. You can think of it as a way to simplify code by focusing on what objects have in common, rather than their individual differences. Abstraction helps to make code more modular, reusable, and easier to maintain. So, instead of dealing with individual objects, we create abstract classes that define the common features of related objects. This way, we can write more generic code that can handle a variety of objects, rather than having to write specific code for each one.

Question 31

Through abstraction, we hide

Answer 31

underlying complexity through a simplified interface

Question 32

What is encapsulation?

Answer 32

involves bundling related data and behavior into a single unit called a class, and hiding it from other parts of the program. You can think of it like a box that contains everything related to an object and controls access to it. This helps to prevent external interference that could potentially cause the object to become invalid or inconsistent. Encapsulation allows for better organization, modularity, and security of code. It also makes it easier to change the implementation details of a class without affecting the rest of the program. So, to sum up, encapsulation is about bundling data and behavior together, and hiding it from the rest of the program to ensure data integrity and security.

Question 33

What does encapsulation mean?

Answer 33

Restricting access to data members by using access modifiers and getter/setter methods

Question 34

Encapsulation means that data should only be accessed through setter and getter methods T/F

Answer 34

True

Question 35

An interface is similar to an abstract class, but one of many differences is that

Answer 35

a class can only inherit one other class, but a class can implement as many interfaces as it needs.

Question 36

Interfaces have these advantages over class

Answer 36

Implementation details do not need to be provided in the interface.

A class can only extend one other class, but it can implement as many interfaces as needed.

Question 37

Interfaces have implicit modifiers on methods and variables:

Answer 37

Methods are ‘public’ and ‘abstract’
Variables are ‘public’, ‘static’, and ‘final’

Question 38

Which is NOT a true statement about the Java programming language?
A class can inherit from multiple classes
A class can only inherit from one class
Interfaces are created using the implements keyword
A class can implement any interfaces as needed.

Answer 38

A class can inherit from multiple classes

Question 39

To inherit interfaces, a class must implement them and they are REQUIRED to implement all methods, unless the class is ___?

Answer 39

abstract

Question 40

Interfaces have implicit modifiers on methods and variables. Which of these are NOT one of those implicit modifiers?
virtual
public
static
final

Answer 40

virtual

Question 41

Comparable is an interface which defines

Answer 41

the natural ordering for a class. A class must implement Comparable if it is to be sorted by the compareTo() method.