Review of OOP

• Object-Oriented Programming (OOP)


  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
• Structure of Object Oriented Programming

  • 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

  
• Main Principles of OOP

  • 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.
• Encapsulation


  Containing information in an object, exposing only selected information
• Advantages of Encapsulation

  • Data Hiding: The user will have no idea about the inner implementation of the class
  • Increased Flexibility: We can make the variables of the class read-only or write-only
  • 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
• Abstraction


  The process of hiding certain details and showing only essential information to the user
• Abstract Classes and Abstract Methods

  • An abstract class is a class that is declared with an abstract keyword
  • An abstract method is 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
  • A method defined abstract must always be redefined in the subclass, thus making overriding compulsory OR either make the subclass itself abstract
  • 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
• Polymorphism


  The ability of a message to be displayed in more than one form
• Types of Polymorphism in Java

  • Compile-time Polymorphism (Static Polymorphism): Achieved by function overloading or operator overloading
  • Runtime Polymorphism (Dynamic Method Dispatch): A process in which a function call to the overridden method is resolved at Runtime
• Abstraction


  can be achieved with either abstract classes or interfaces.
• Encapsulation


  is defined as the wrapping up of data under a single unit. It is the mechanism that binds together code and the data in manipulates.