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Low Level Design Basics

Object-Oriented Programming

• Object-Oriented Programming: A style of programming that focuses on using objects to design and applications.
• Procedure-Oriented Programming: Programs are designed as blocks of statements to manipulate data.

• OOP organizes the program to combine data and functionality and wrap it inside object.

• Object: Represents a real world entity and the basic building block of OOP.
  • Example: Online Shopping System - Shopping Cart, Customer, Product Item are some of objects.
• Class: Prototype or blueprint of an object. Template definition of the attributes and methods of object.
  • Example: Online Shopping System - Customer Object will have attributes like name, shipping address, cards etc.. and methods for placing order, cancel order etc.

4 Principles of Object-Oriented Programming

1. Encapsulation:
   • Mechanism of binding the data together and hiding it from outside world.
   • Achieved when each object keeps its state private so that other objects don’t have direct access to its state.
   • This state can only be accessed through a set of public functions.
2. Abstraction:
   • Can be thought as a natural extension of encapsulation.
   • It means hiding all but the relevant data about an object to reduce the complexity of the system.
   • In a large system, objects talk to each other, which makes it difficult to maintain a large code base.
   • Abstraction helps by hiding internal implementation details of objects and only reveals operations that are relevant to other objects.
3. Inheritance
   • Mechanism of creating new classes from existing ones.
4. Polymorphism
   • It is the ability of an object to take diffferent forms.

OO Analysis and Design

• A structured method for analyzing and designing a system by applying object-oriented concepts.
• An investigation into the objects constituing the system.
• Starts by first identifying the objects of the system and then figuring out the interactions b/w the various objects.

Process of OO Analysis and Design

1. Identifying the objects in the system.
2. Defining the relationship b/w objects.
3. Establishing the interface of each object.
4. Making a design that can be converted to executables (code) using OO languages.

Standard Method / Modeling Tool to document all these informations

• We use UML (Unified Modeling Language) to document/ model these informations.
• UML can be considered as the succesor of the OO Analysis and Design.
• Powerful enough to represent all the concepts that exists in OO Analysis and Design.
• UML diagrams are representation of OO concepts.

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