IntroductionA Little background

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Few Terminologies

Basic OOP Cohesion Coupling

Code Smells Design Smells Technical Debt

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Cohesion

Cohesion refers to what the class (or module) will do Try to achieve High Cohesion

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Coupling

How related are two classes / modules and how dependent they are on each other Try to achieve Loose Coupling

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Code Smells

Duplicate code Long method Large class Temporary field Switch statements Parallel inheritance hierarchies

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Design Smells

Rigidity Software is difficult to change

Fragility Program breaks in many places when a change mode in a single place

Immobility Parts could be useful in other systems, but effort and risk to separate from original system is

too great.

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Design Smells

Viscosity Design-preserving methods are more difficult to use than the hacks Development environment is slow and inefficient

Needless complexity Contains elements that aren’t currently useful

Needless repetition System has lots of repeated code elements

Opacity A module is difficult to understand

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Technical Debt

The cost to fix rotting code Interest charges build over time The longer we take to remove the smells, the more it will cost

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End of Introduction

So Now, Let’s begin…

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SOLID Principles - ISRP – Single Responsibility PrincipleO/CP – Open Closed Principle

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What are SOLID Principles ?

Single responsibility Open-closed Liskov substitution Interface segregation Dependency inversion

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First five principles named by Robert C Martin in early 2000.

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Why SOLID ?

When Applied together it creates a system Easy to Maintain Easy to Extend over time

To remove the Code Smells Part of overall strategy of agile and adaptive programming

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Why Solid ? Another View

To Deliver Fast To manage changes easily To deal with complexity

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Single Responsibility Principle

A software module should have one  and only one responsibility

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Example

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Is SRP Violated Here ?

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Is SRP Violated Here ?

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Real world SRP

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SRP - Summary

SRP is the simplest of the principles, and one of the hardest to get right We tend to join responsibilities together It's usually hard to see different  responsibilities

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Open / Closed Principle

All systems change during their life cycles avoid a cascade of changes to dependent modules When requirements change, you extend the behavior, not changing old code

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Open / Closed Principle

Software Entities ( Classes, Modules, Functions Etc.) Should be open for extension but closed for modification

Open for extension Behavior of the module can be extended We are able to change what the module does

Closed for modification Extending behavior does not result in changes to source, binary, or code of the module

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Is O/CP Violated Here ?

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Solution

Open / Closed Rule of Thumb

Use IF/SWITCH statements if number of cases are unlikely to change

Use strategy pattern when number of cases are likely to change

Don’t code for situations that you won’t ever need More smaller class files != more complicated code

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End of Presentation