Java and Object-Oriented Programming

Introduction to Object-Oriented Programming (OOP)

• OOP is one of three programming paradigms, along with Procedural and Functional Programming.
• A programming paradigm refers to different approaches to structuring and organizing code.
• The term "paradigm" is synonymous with "pattern".

Procedural Programming

• Operations are executed one after another in a sequence.
• Variables are used to refer to named computer memory locations that hold data.
• Data is stored in a location and can be used for decisions, arithmetic, or output.
• The data stored in a variable can change during program execution.
• Basic construct is blocks of code called "procedures".
• Procedures are grouped into logical units based on individual operations.
• Procedures are also called functions, modules, subroutines, and methods (commonly in Java).
• A procedural program can pause to call a procedure and temporarily suspend the current logic.
• BASIC, C, C++, and Pascal support this paradigm.

Functional Programming

• This style builds programs by focusing on declarations and expressions rather than the execution of statements.
• Aims for code that is clearer and bug-resistant by avoiding flow-control statements.
• Functions are the basic units and are treated as first-class citizens.
• Functions can be assigned to a variable, passed as an argument, or returned from a function.
• Erlang, Scala, Haskell, and Elm support this paradigm.

Object-Oriented Programming (OOP)

• This is an extension of procedural programming.
• Employs a different approach to writing computer programs.
• Objects, which model objects in the real world, are the main building blocks.
• OOP was developed to eliminate the limitations of other paradigms.
• OOP makes programming more flexible, user-friendly, and less complex.
• Includes creating blueprints for objects (classes).
• Involves creating specific instances of those classes (objects).
• Creates applications that manipulate or use these objects.
• Java, Python, VB.NET, and C# support this paradigm.

Naming Conventions

• Procedural Programming uses Variables, User-defined Data Types, Structured Members, Functions, and Function Calls.
• Object-Oriented Programming uses Objects, Classes, Instance Variables, Methods, and Message Passing.

Differences Between Procedural and OOP

• Procedural Programming emphasizes procedures rather than data.
• Object-Oriented Programming emphasizes data rather than procedures.
• In Procedural Programming, data is not secured
• In Object-Oriented Programming, data is secured
• Procedural Programming uses a top-down approach.
• Object-Oriented Programming uses a bottom-up approach.
• Procedural Programming does not model real-world entities.
• Object-Oriented Programming models real-world entities.
• Procedural Programming decomposes programs into functions or procedures.
• Object-Oriented Programming decomposes programs into objects.

Advantages of OOP

• Programs are modularized by using classes and objects.
• Reduces code duplication and promotes reusability by allowing related objects to share code.
• Provides data security through encapsulation, making data inaccessible and unmodifiable by non-member functions.
• Reduces program complexity through inheritance.
• Reduces the time for creation and ease of OOP code implementation.

OOP Concepts: Class

• It is a group or collection of objects with common properties.
• Serves as the basic unit of programming in OOP.
• User-defined data type that stores complex data.
• It is like a blueprint that exists before any houses are built.
• A class definition describes what attributes objects will have and what those objects can do.
• An attribute details the characteristics of an object, serving as its properties.

OOP Concepts: Object

• It is a specific and concrete instance of a class.
• An identifiable entity with characteristics and behavior.
• A person, place, or table of data, and any real-world entity with existence.
• Data Members and Operations called Function Members are features.
• A smartphone's color, weight, and price are data members; making video calls, taking photos, or recording audio are function members.

OOP Concepts: Method

• Classes define the methods their objects can use, other than defining properties.
• A method is a self-contained block of program code that carries out actions and is similar to a procedure in Procedural Programming.

Class, Object, and Method Examples

• Class: Automobile; Object: Make, Model, Year, Color; Method: Forward, Backward, Gas Status.
• Class: Dog; Object: Breed, Name, Age, Vaccine; Method: Walking, Eating, Name Recognition.
• Object's class helps understand its characteristics.
• Objects are like nouns, methods are like verbs.

Data Abstraction

• Includes only essential details of an entity without including background details.
• Focuses on using features rather than internal workings.
• Hidden information is called abstracted data.

Data Encapsulation

• Wraps up data and functions into a class.
• Performs data hiding, which insulates data from outside programs.
• Data is not directly accessible outside the class, except through defined functions.

Inheritance

• The ability to create classes—the new classes—that share the attributes and methods of existing classes but with more specific features.
• The original class is a base class, parent class, or superclass.
• The new class is a derived class, child class, or subclass.
• Derived classes inherit properties from the base class.

Polymorphism

• Poly means many, while morph means forms.
• Languages allow the same word or symbol to be interpreted correctly in different situations based on the context.
• Examples include operator overloading and function overloading.

Operator Overloading

• Making an operator perform tasks in different instances.
• Using the addition (+) operator as an arithmetic operator or as a string concatenation operator.

Function Overloading

• Process of using two or more functions with the same name but with different return types or numbers of arguments.
• Such as: paint() furniture, paint() vehicle, and paint()building.

Methods Specifics

• Method is a program module that contains a series of statements that carries out a task and can be be called unlimited times.
• Main() method executes automatically when a program is run, and can execute additional methods.
• To execute a method, it is called or invoked.
• A calling method, or client method, invokes a called method.

Method Header

• Or method declaration, provides information about how other methods can interact with it.

Elements Of A Method Header

• public-an access modifier that allows any other class to use it.
• static-used when any method can be used without instantiating an object.
• void – a return type used when a method returns no data.
• Method Name can be any legal identifier for classes and variables.
• Parentheses – contains data to be sent to the method.

Method Body

• Contains the statements that carry out the work of the method.
• The method body is found between a pair of curly braces, and is called its implementation.

Method Placement

• Methods can be placed within a class, but outside of any other methods.

Method Order

• The main() method is always executed first in any Java application.
• The order in which the methods are called is what makes a difference in how an application executes.

Separate Methods

• A complete name that includes the class is a fully qualified identifier.
• Using a method call makes the main() method short and easy to follow.
• Using a well-named method makes it easy to see the overall intent of the separate println() statements.
• Methods are easily reusable.

Java Classes

• Java classes can be classified into the following types: Classes from which objects are not instantiated and Classes from which objects are created
• With OOP, a class can be created to and run as an application to instantiate objects from them and do both.
• When creating a class, a name must be assigned to it, and the data and methods that will be part of the class must be determined.
• A class header has three (3) parts: an optional access specifier, the keyword class, and any legal identifier in naming the class

Data fields

• The data components of a class are called data fields that are declared variables within a class but outside any method.
• A data field is static if it occurs once per class and non-static if it happens once per object.
• Assigning private access to a field means that no other classes can access the field's values except the methods of the same class.
• The principle used in creating private access is referred to as information hiding, an important component of object-oriented programs.

Methods

• Classes that instantiate objects contain both fields and methods.
• Methods that retrieve values are called accessor methods or getters that conventionally start with the prefix get.
• Methods that set or change field values are called mutator methods or setters that conventionally start with the prefix set.

Declaring Objects

• A two-step process is involved in creating an object that is an instance of a class: type and an identifier are supplied, and computer memory is allocated for that object.
• A new operator should to allocate the memory for an object such.
• Employee now also becomes a reference type as opposed to built-in types like int, which are primitive types.
• In object-oriented programming, a constructor is a special type of method that creates and initializes objects.
• After an object has been instantiated, the methods can be accessed using the object's identifier, a dot, and a method call.

Explore key concepts in Java and the principles of Object-Oriented Programming (OOP). Understand classes, objects, methods, and access modifiers. Learn about static methods and the main method in Java.