Computer programming 2

• Object-oriented Programming (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, with "paradigm" synonymous with "pattern".

Procedural Programming

• Operations are executed sequentially, defining and using variables that refer to named computer memory locations.
• Data can be read from input, stored, used in decisions or arithmetic, or sent to output, and can change during program execution.
• The basic construct is blocks of code called "procedures," which are grouped logical units based on individual operations.
• Procedures are also known as functions, modules, subroutines, and methods.
• Procedural programs can pause to call a procedure, temporarily suspending the current logic.
• BASIC, C, C++, and Pascal support this paradigm.

Functional Programming

• Computer programs are built by focusing on declarations and expressions rather than the execution of statements.
• Functional programming aims for clearer, bug-resistant code by avoiding flow-control statements like for, while, break, continue, and goto.
• Functions are the basic units and are treated as first-class citizens: they can be assigned to a variable, passed as an argument, or returned from a function.
• Erlang, Scala, Haskel, and Elm support this paradigm.

Object-Oriented Programming (OOP)

• It extends procedural programming with a different approach to computer programs, using objects to model real-world objects.
• OOP was developed to overcome the limitations of other paradigms, aiming for more flexible, user-friendly programming.
• Writing OOP involves creating classes (blueprints for objects), creating objects (specific instances of classes), and creating applications that manipulate these objects.
• Java, Python, VB.NET, and C# support OOP.

Naming Conventions

• Procedural Programming relates to:
  • Variables as Objects
  • User-defined Data Types as Classes
  • Structured Members as Instance Variables
  • Functions as Methods
  • Function Call as Message Passing

Procedural vs. Object-Oriented Programming

• Procedural Programming:
  • Emphasizes procedures over data.
  • Data isn't secured.
  • Uses a top-down approach.
  • It does not model real-world entities
  • Decomposes programs into functions or procedures
• Object-oriented Programming:
  • Emphasizes data over procedures.
  • Data is secured.
  • Uses a bottom-up approach.
  • Models real-world entities.
  • Decomposes programs into objects

Advantages of OOP

• Programs are modularized using classes and objects.
• Code duplication is reduced, and reusability is increased through linking code and objects.
• Data security is enhanced through encapsulation, making data inaccessible and unmodifiable to non-member functions.
• Program complexity is reduced through inheritance.
• Creation and implementation of OOP code is faster.

OOP Concepts

Class

• A group or collection of objects with common properties and a user-defined data type for storing complex data.
• Analogous to a blueprint before houses are built or a recipe before bread is baked.
• A class definition describes the attributes and behaviors of its objects; attributes define an object's characteristics and serve as properties.

Object

• A specific and concrete instance of a class; an identifiable entity with characteristics and behavior, like a person, place, or table of data.
• Real-world entities possess data members (features) and function members (operations).

Method

• Classes define the methods their objects can use, similar to procedures in Procedural Programming.

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

Data Abstraction

• Including only essential details of an entity, excluding background details.
• For example, focusing on using a smartphone's Bluetooth and camera features without concerning how they work internally.
• The hidden information is called abstracted data.

Data Encapsulation

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

Inheritance

• Creating classes that share attributes and methods of existing classes but with more specific features.
• The class that inherits properties is the base class, parent class, or superclass.
• The class that inherits from another is the derived class, child class, or subclass.

Example of Inheritance

• Employees are the base class, while Manager, Supervisor, and Clerk are derived classes.
• The employee base class inherits properties from the derived classes, with each derived class having its own properties.

Polymorphism

• Describes the feature of languages that allows the same word or symbol to be interpreted correctly in different situations based on context.
• Includes operator overloading and function overloading.

Operator Overloading

• Making an operator perform tasks in different instances.
• I.e., the addition (+) operator can perform arithmetic addition or string concatenation.

Function Overloading

• Having two or more functions with the same name but different return types or numbers of arguments.

Methods

• A program module containing a series of statements that carry out a task that can be invoked multiple times.
• To execute, a programmer calls or invokes the method.
• In other words, a calling method, or client method, invokes a called method.
• The main() method, such as public static void main(String[] args), provides information about how other methods can interact with it.

Method Header Components

• public - An access modifier that allows any other class to use it and not just in the class in which the method resides. Other access modifiers include private, protected, and package if left unspecified.
• static – Used when any method can be used without instantiating an object or not requiring an object when they are called.
• void - A return type used when a method returns no data. A return type describes the data type the method sends back to its calling method.
• Method Name - Must be one word with no spaces, cannot be a Java keyword, and usually contains a verb.
• Parentheses – Contains data to be sent to the method. When a main() method is written in a class, the parentheses in its header surround String[] args.
• Method Body - The statements that carry out the work of the method. It is found between a pair of curly braces and called its implementation.

Method Placement and Execution

• Methods must be written in the program but outside of other methods, they can never overlap.
• The order in which methods appear does not matter, except that the main() method is always executed first.
• A fully qualified identifier includes the class name, a dot, and the method name (e.g., CompanyInfo.displayHours()), and is necessary if the same method is used in another class.

Advantages of Creating a Separate Method

• Using a method call to execute different println() statements 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.
• AS methods are easily reusable, they can be used in any application that needs that specific action in the program.

Classes and Objects

• Java classes can be classified into the following types:
  • Classes from which objects are not instantiated, such as the programs with the main() methods
  • Classes from which objects are created
• With OOP, a class can be created to 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, starting with an uppercase letter (e.g., public class Employee).
• Data components of a class are called data fields and 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.
• Private access specifier provides the highest security level, meaning 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.
• Accessor methods or getters retrieve values and conventionally start with the prefix get.
• Mutator methods or setters set or change field values and conventionally start with the prefix set.

Declaring Objects

• Object declaration involves two steps: supplying a type and identifier, and allocating computer memory.
• The new operator allocates memory for an object.
• A constructor is a special type of method that creates and initializes objects.
• Java writes constructors even when a user does not.
• After instantiation, methods are accessed using the object's identifier, a dot, and a method call.