OOP Midterms

Object-oriented programming

a computer programming model that organizes software design around data, or objects rather than functions and logic.

Object

a data field that has unique attributes and behavior.

Benefits of OOP

Reusability, scalability, and efficiency

Data Modeling

• First step in OOP

• collect all of the objects a programmer wants to manipulate and identify how they relate to each other

Example of OOP

• The object is a human being, who is described by properties like name and address.

Classes

• are user-defined data types that act as the blueprint for individual objects, attributes, and methods

Objects

• are instances of a class created with specifically defined data.

• when class is defined initially, the description is the only _____ that is defined.

Methods

• are functions that objects can perform.

• they are defined inside a class that describe the behaviors of an object.

Instance Methods

subroutines contained in an object

Attributes

• represent the state of an object

• they are the characteristics that distinguish classes.

Encapsulation

• states that all important information is contained inside an object and only select information is exposed.

• the implementation and state of each object are privately held inside a defined class.

Abstraction

objects only reveal internal mechanisms that are relevant for the use of other objects, hiding any unnecessary implementation code.

Inhertiance

• classes can reuse code and properties from other classes

• relationships and subclasses between objects can be assigned, enabling developers to reuse common logic while still maintaining a unique hierarchy.

Polymorphism

• objects are designed to share behaviors, and they can take on more than one form.

• The program determines which meaning or usage is necessary for each execution of that object from a parent class, reducing the need to duplicate code.

• enables different types of objects to pass through the same interface.

Syntax

set of rules that define how words and punctation are organized in a programming language

Coupling

• is the degree to which software elements are connected to one another.

• if a class has its attribute change, then any other coupled class also changes.

Association

• is the connection between one or more classes.

• can be one to one, many to many, one to many or many to one

Advantages of OOP

• Modularity

• Reusability

• Flexibility and Extensibility

• Encapsulation

• Abstraction

Modularity

• breaking down a complex system intro smaller, manageable units (classes and objects).

• Each class represents a specific functionality, making it easier to understand, maintain, and update the codebase.

Reusability

• OOP facilities code ______ through inheritance and polymorphism.

• inheritance allows a subclass to inherit properties and behaviors from a superclass, reducing code duplication

• Polymorphism enables objects to be treated as instances of their superclass, enhancing flexibility and extensibility,

Flexibility and Extensibility

• provides ____ and ___ by allowing developers to add new features or modify existing ones without affecting the entire codebase.

Encapsulation

is the key principle of OOP that encapsulates data (attributes) and methods (functions) with a single unit (class).

Abstraction

focuses on hiding complex implementation details and exposing only essential features to users.

Simula

the first object-oriented programming language

Pure OOP languages

• Ruby

• Scala

• JADE

• Emerald

Primarily for OOP Languages

• Java

• Python

• C++

Languages that pair with OOP

• Visual Basic.NET

• PHP

• JavaScript

Benefits of OOP

• Modularity

• Reusability

• Productivity

• Easily upgradable and scalable

• Interface Descriptions

• Security

• Flexibility

• Code maintenance

• Lower cost

Encapsulation

• is a fundamental OOP principle that combines data and methods class

• it allows implementation details to be hidden while exposing a public interface for interaction.

Example of Encapsulation

How encapsulation is implemented

• by declaring instance variables as private, restricting direct access.

• public getter methods retrieve variable values, while setter methods modify them, enabling controlled access.

Encapsulation

• is defined as the wrapping up of data under a single unit.

• the variables or data of class are hidden from any other class and can be accessed only through any member function of its own class.

Private class

can hide its members or methods from the end user, using abstraction to hide implementation details, by combining data hiding and abstraction.

How to achieve encapsulation?

by declaring all the variables in the class as private and writing public methods in the class to set and get values of variables.

Inheritance

a mechanism in java by which one class is allowed to inherit the features (fields & methods) of another class.

Reasons on why we need Java Inheritance

• Code Reusability

• Method Overriding

• Abstraction

Class

• is a set of objects which shares common characteristics/behavior and common properties/attributes.

• a blueprint or prototype from which objects are created.

Super Class/Parent Class

the class whose features are inherited is known as a superclass. (or base class/parent class)

Sub Class/Child Class

• the class that inherits the other class is known as a subclass (or a derived class, extended class or child class).

• has its own fields and methods on addition to the superclass fields and methods.

Reusability

• inheritance supports the concept of “______”

• when we want to create a new class and there is already a class that includes some of the code that we want, we can derive our new class from the existing class.

How to use inheritance in Java?

• the extends keyword is used for ______ in java.

• Using the extends keyword indicates you are derived from an existing class.

Subclass

During inheritance only the object of the _____ is created, not the superclass.

Types of Inheritance

1. Single Inheritance

2. Multilevel Inheritance

3. Hierarchical Inheritance

4. Multiple Inheritance

5. Hybrid Inheritance

Single Inheritance

• a sub-class is derived from only one super class.

• it inherits the properties and behavior of a single-parent class

Multilevel Inheritance

• a derived class will be inheriting a base class, and as well as the derived class also acts as the base class for other classes.

Hierarchical Inheritance

one class serves as a superclass for more than one subclass.

Multiple Inheritance (Through Interfaces)

• one class can have more than one superclass and inherit features from all parent classes.

• note: java does not support ______ inheritances with classes. this is only achievable through interfaces.

Hybrid Inheritance

• is a mix of two or more of the above types of inheritance.

• java does not support multiple inheritances with classes, ______ inheritance involving multiple inheritance is also not possible with classes.

• it can be achieved through a combination of multilevel inheritance and hierarchical inheritance with classes, hierarchical and single inheritance with classes.

IS-A

is a way of saying: this object is a type of that object.

Sub-classes

in _____ we can inherit members as is, replace them, hide them, or supplement them with new members

Inherited Fields

The _____ ____ _can be used directly, just like any other fields.

New fields

We can declare ____ ____ in the subclass that are not in the superclass.

Inherited Methods

• The _____ methods can be used directly as they are.

Instance Method

We can write a new _____ ____ in the subclass that has the same signature as the one in the superclass, thus overriding it.

Static method

W can write a new ____ ___ in the subclass the same signature as the one in the superclass, thus hiding it.

New methods

We can declare ____ ___ in the subclass that are not in the superclass.

Subclass Constructor

We can write a _____ ____ that invokes the constructor of the superclass, either, implicitly or by using the keyword super.

Advantages of Inheritance in Java

1. Code Reusability

2. Abstraction

3. Class Hierarchy

4. Polymorphism

Disadvantages of Inheritance in Java

1. Complexity

• can make the code more complex and harder to understand.

1. Tight Coupling

• creates a tight coupling between the superclass and subclass, making it difficult to make changes to the superclass without affecting the subclass.

Default Superclass

every class has one and only one direct ________ (single inheritance). In the absence of any other explicit _______, every class is implicitly a subclass of the Object class.

Super class can only be one

can have any number of subclasses but only one superclass.

Inheriting Constructors

inherits all the members (fields, methods, and nested classes) from its superclass.

Private member inheritance

• a subclass does not inherit the private members of its parent class.

• however, if the superclass has public or protected methods (getters and setters) for accessing its private fields, these can also be used by the subclass.

Polymorphism

• means ‘having many forms’

• refers to the ability of a message to be displayed in more than one form

• it allows objects to behave differently based on their specific class type.

Types of Java Polymorphism

• Complie-Time Polymorphism

• Runtime Polymorphism

Compile-Time Polymorphism

• also known as static polymorphism

• is achieved by function overloading or operator overloading. (but java doesnt support operator overloading.

Method Overloading

• when there are multiple functions with the same name but different parameters then these functions are said to be overloaded.

• functions can be overloaded by changes in the number of arguments or/and a change in the type of arguments.

Subtypes of Compile-time Polymorphism

• Function overloading

• Operator overloading

• Template

Function Overloading

a feature in c++ and java where multiple functions can have the same name but with different parameter lists. the compiler will decide which function to call based on the number and types of arguments passed to the function.

Operator Overloading

a feature in c++ where the operators such as +, -. *, etc. can be given additional meanings when applied to user-defined data types.

Template

• is a powerful feature in C++ that allows us to write generic functions and classes.

• is a blueprint for creating a family of functions or classes.

Runtime Polymorphism

• is known as dynamic method dispatch

• a process in which a function call to the overridden method is resolved at runtime.

• this can be done method overriding

Subtype of Run-Time Polymorphism

Virtual Functions

Virtual Functions

• allows an object of a derived class to behave as if it were an object of the base class.

• the derived class can override the _____ ____ of the base class to provide its own implementation.

• the function call is resolved at runtime, depending on the actual type of object.

Advantages of Polymorphism

Disadvantages of Polymorphism

Subtyping vs Subclassing

• OOP relies heavily on concepts of subtyping and subclassing.

• Understanding these concepts is crucial for effectively writing reusable and maintainable code.

Subclassing

• is a specific mechanism in OOP languages like Java that implements subtyping through inheritance.

• inherits the attributes and methods of its superclass, establishing an “is-a” relationship

Subtyping

• is a broader concept that deals with relationships between types.

• it’s about the ability of one type to be substituted for another type in certain context.

• is primarily achieved through inheritance and interfaces

Benefits of Subtyping with Interfaces

Subclassing

• is a specific implementation of subtyping through class hierarchies

• involves creating a new class that inherits attributes and behaviors from an existing class, known as a superclass.

Key Characteristics of Subclassing

Subtyping without Subclassing

Polymorphism via Interfaces

Abstraction

• is the process of hiding the implementation details and only showing the essential functionality or features to the user.

• this helps simplify the system by focusing on what the object does rather than how it does it.

How is abstraction achieved in Java?

• by interfaces and abstract classes.

Abstract Class

• is a class that is declared with an abstract keyword.

• may or may not have all abstract methods. some of them can be concrete methods

• can have parameterized constructors and the default constructor is always present in an abstract class.

Abstract Method

• is a method that is declared without implementation

• must always be redefined in the subclass, thus making overriding compulsory or making the subclass itself abstract.

Class

any ____ that contains one or more abstract methods must also be declared with an abstract keyword.

Instantiated

There can be no object of an abstract class. That is, an abstract class can not be directly ______ with the new operator.

Algorithm to Implement Abstraction

Advantages of Abstraction

• simplifies complex systems by hiding implementation details.

• increases code reusability and maintainability

• enhances security by exposing only essential features

• improves modularity and separation of concerns.

• provides a clear and user-friendly interface.

Disadvantages of Abstraction

• it can add unnecessary complexity if overused.

• may reduce flexibility in implementation.

• makes debugging and understanding the system harder for unfamiliar users.

• overhead from abstraction layers can affect performance.

Why do we use abstract?

it is used to simplify the complexity and make easier for both user and end users. we can use abstraction to hide details and show necessary parts.