INTRODUCTION TO OOP

Question 1

Describe object-oriented programming

Answer 1

A method of programming based on a hierarchy of classes with well defined and cooperating objects.

Question 2

What is an object?

Answer 2

An object is an executable copy of a class. It can also be referred to as an instance

Question 3

What are states and behaviors, give real world examples

Answer 3

For a dog:
states (breed, color, age, hungry) - nouns and adjectives
behaviors (barking, eating, fetching) -verbs

Question 4

What are fields and methods?

Answer 4

• An object stores its state in fields and exposes its behavior through methods.
• Methods operate on an object’s internal state and IMPLEMENT object-to-object communication.

Question 5

What is a class?

Answer 5

A blueprint from which objects are created. It defines the data and the methods to work on the data

Question 6

What is a package and what is its importance?

Answer 6

• A package is a namespace that organizes a set of related classes and interfaces. (It is like different folders on our personal computer.)
• Packages are important for organization.

Question 7

Where can one find a complete listing of all packages, interfaces, classes, fields, and methods supplied by the Java SE platform.

Answer 7

The Java Platform API Specification

*application programming interface

Question 8

What is an interface?

Answer 8

• An interface is a group of related methods with empty bodies.
• Methods form the object’s interface with the outside world; e.g remote buttons, computer keyboards, e.t.c.

Question 9

What are some characteristics of OOP?

Answer 9

1. Encapsulation
2. Inheritance
3. Abstraction
4. Polymorphism
5. Message passing
6. Garbage collection

Question 10

Define encapsulation

Answer 10

• This is a concept that enables the hiding unnecessary details in classes and only providing a clear and simple interface for working with them.
• It is also called information hiding.
• An object must provide its users only with the essential information for manipulation, without the internal details.

Question 11

What is inheritance

Answer 11

• Inheritance is a concept in OOP that enables new objects to take on the properties of existing objects.
• Object-oriented programming allows classes to ASSUME commonly used state and behavior from other classes.
• Inheritance is an “is a” relationship eg a dog is a animal; therefore it inherits the characteristics common to animals

Question 12

What are the names of classes involved in inheritance?

Answer 12

• A class that is used as the basis for inheritance is called a superclass or base class.
• A class that inherits from a superclass is called a subclass or derived class.
• In Java, each class is allowed to have one direct superclass, and each superclass has the potential for an unlimited number of subclasses

Question 13

What is abstraction?

Answer 13

The process of representing essential features without including background details or explanations / The process of defining the essential concepts while
ignoring the inessential details.

Question 14

What are the types of abstraction?

Answer 14

• Data Abstraction
• Functional Abstraction
• Object Abstraction

Question 15

What is polymorphism?

Answer 15

This is the ability to present the same interface for differing underlying forms.

Question 16

What are the different types of polymorphism?

Answer 16

• Method overloading

* Method overriding

Question 17

Describe garbage collection in OOP

Answer 17

This is a form of automatic memory management whereby the garbage collector attempts to reclaim garbage, or memory occupied by objects that are no longer in use by the program.

Question 18

What is a variable?

Answer 18

A variable is a container that holds values that are used in a Java program

Question 19

What are the different types of variables?

Answer 19

• Instance variables (non-static fields)
• Class variables (static fields)
• Local variables
• Parameters

Question 20

Describe an instance variable (non-static field)

Answer 20

• Objects store their individual states in “non-static fields” (fields declared without the static keyword.)
• Non-static fields are also known as instance variables because their values are unique to each instance of a class (object)
• E.g., the different ages of new objects in a Registration system.
*immediately after class

Question 21

Describe a class variable (static fields)

Answer 21

• A class variable is any field declared with the static modifier.
• There is exactly one copy of this variable in existence in a class regardless of how many times the class has been instantiated.
• The key word static is usually used to indicate static variables.
*immediately after class
EG static int data = 30;

Question 22

Describe local variables

Answer 22

• These are variables that store temporary states.
• There is no special keyword designating a variable as local.
• Local variables are only visible to the methods in which they are declared; they are not accessible from the rest of the class.
*Found within a method

Question 23

What are parameters and where are they found?

Answer 23

• These are variables found within the parenthesis of different structs within a program.
• Examples of the structs where parameters are found include:
• Methods
• Constructors
*Found within ()

Question 24

Give example (source code) showing the different types of variables

Answer 24

public class A  
{  
    static int m=100;/static variable  
    void method()  
    {    
        int n=90;/local variable    
    }  
    public static void main(String args[])  
    {  
        int data=50;/instance variable    
    }  
}//end of class

Question 25

What are the rules for naming variables?

Answer 25

1. Variable names are case-sensitive.
2. Can begin with a letter, underscore or $
3. Subsequent characters for a variable may be letters, digits, dollar signs, or underscore characters.
4. When choosing a name for your variables, use full words instead of cryptic abbreviations
   (self-documentation)
5. Variable names consisting of more than one word should be named, e.g. carSpeed or car_speed

Question 26

What are the eight primitive data types in java?

Answer 26

• Byte
• Short
• Integer
• Long
• Float
• Double
• Boolean
• Character

Question 27

What do data types determine?

Answer 27

the values it may contain, their sizes plus the operations that may be performed on it.

Question 28

Define states and behaviors

Answer 28

States/attributes- built in characteristics of an object

behaviors- predefined functions

Question 29

Briefly explain at least 4 object-oriented design concepts.

Answer 29

encapsulation, abstraction, inheritance, and polymorphism

Question 30

why is java suitable for studying advanced OOP / What are the advantages of java?

Answer 30

1. Java is simple. It is easy to learn, understand and debug.
2. It makes it possible to write reusable and modular code
3. Java reduces security threats and risks by avoiding the use of explicit pointers
4. Java programs are cheap to develop and maintain as these programs are dependent on a specific hardware infrastructure to run. We can easily execute them on any machine that reduces the extra cost to maintain.
5. Java offers a very effective boon to its users by providing the feature of platform independence that is Write Once Run Anywhere(WORA) feature.
6. Java provides Automatic Garbage Collection run by the java virtual machine

Question 31

What are the disadvantages of java?

Answer 31

1. Java is slow and has a poor performance due to the extra level of compilation and abstraction by the JVM.
2. Java provides no backup facility. Java mainly works on storage and not focuses on the backup of data
3. Java requires a significant or major amount of memory space as compared to other languages like C and C++
4. Java codes are verbose, meaning that there are many words in it and there are many long and complex sentences that are difficult to read and understand. This can reduce the readability of the code.