Basics

• Object-oriented programming (OOP) is a computer programming model that organizes software design around data, or objects, rather than functions and logic.
• An object can be defined as a data field that has unique attributes and behavior.
• 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. Objects can correspond to real-world objects or an abstract entity.
• Methods are functions that are defined inside a class that describe the behaviors of an object.
• Attributes are defined in the class template and represent the state of an object.
• Encapsulation: containing information in an object, exposing only selected information
• Inheritance: child classes inherit data and behaviors from parent class
• Abstraction: only exposing high level public methods for accessing an object
• Polymorphism: many methods can do the same task
• Data Hiding: The user will have no idea about the inner implementation of the class. It will not be visible to the user how the class is storing values in the variables.
• Increased Flexibility: We can make the variables of the class read-only or write-only depending on our requirement.
• Reusability: Encapsulation also improves the re-usability and is easy to change with new requirements.
• Testing code is easy: Encapsulated code is easy to test for unit testing.
• Encapsulation is defined as the wrapping up of data under a single unit. It is the mechanism that binds together code and the data it manipulates.
• Data abstraction is the process of hiding certain details and showing only essential information to the user.
• Abstraction can be achieved with either abstract classes or interfaces
• Abstract class


  A class that is declared with an abstract keyword
• Abstract method

  A method that is declared without implementation
• An abstract class may or may not have all abstract methods. Some of them can be concrete methods
• Any class that contains one or more abstract methods must also be declared with an abstract keyword
• There can be no object of an abstract class. That is, an abstract class can not be directly instantiated with the new operator
• An abstract class can have parameterized constructors and the default constructor is always present in an abstract class
• The word polymorphism means having many forms. In simple words, we can define polymorphism as the ability of a message to be displayed in more than one form
• Runtime Polymorphism


  It is also known as Dynamic Method Dispatch. It is a process in which a function call to the overridden method is resolved at Runtime.
• Compile-time Polymorphism


  It is also known as static polymorphism. This type of polymorphism is achieved by function overloading or operator overloading