Software Design Principles (SOLID)

Before moving on Design Patterns let's discuss few things about Software Design Principles.


What are Software Design Principles?
Design Principles are set of guidelines that helps to design a software, which needs to avoid these 3 characteristics
  • Rigidity :- Your design is as flexible as it can be. Because if your design is rigid, your minor change will effect majorly in other part of system.
  • Fragility :- It means when you make a change in system, unexpected part of system breaks.
  • Immobility :- Hard to reuse code in another application because its tightly coupled.

and follow these Five Rules (SOLID):-

Single Responsibility Principle 
A class should be designed with one goal but that doesn't mean it will have only one method. It simply means all methods are created to fulfill class goal.
Also if we have more than one reason to change a class and (changes)they are not aligned with class goal, then it is better to split them in more than one class.
Reference :-
http://www.oodesign.com/single-responsibility-principle.html

OCP (Open Closed Principle)
 This is one of the most fundamental principle for a good design software. This principle state that
"Software entities like classes, modules, libraries functions are open for extension but closed for modification". It clearly means once you have created a class or modules it has all work done in it. For further work you can extend it but you can not modify it.
Simple example is use of Abstract class and use concrete class for implementing behavior.
Real-time Example :- You have created a class parse which have basic functionality of parsing data from file. For parsing a Text file, CSV file or XML file you have to extend parser class and create TextParser, CSVParser and XMLParse class  from that, not add additional conditional code in your Parser class.
Reference :-
http://www.oodesign.com/open-close-principle.html

Liskov's Substitution Principle 
It simply states that a derived class can extend feature of Base Class but can not  change feature of Base Class that results in undesired effects.
Reference :-
http://www.oodesign.com/liskov-s-substitution-principle.html

Interface Segregation Principle 
It states that client should not enforce to implement interface's they don't use. So its better to split interface into small interfaces according to their work ethics.
Reference :-
http://www.oodesign.com/interface-segregation-principle.html

Dependency Inversion Principle 
High Level module should not depend on low-level module. Both should depend on Abstraction.
Abstraction should not depend on Details, and detail should not depend on abstractions.
It means a high level class is not directly work with low level module, they are using interface as abstract layer.
Real-time Example :-
Suppose there is a class Manager which needs to take work from class Worker.
So manage will call  work Method of Worker class. But suppose if we need to introduce a new class SuperWorker(super class of ) Worker. Then we need to change implementation of Manager. Dependency Inversion says that we need to create an Interface which had work method and Worker and SuperWorker will implement this method and Manager will call the Method of this Interface instead of calling class method. So the desired class method will automatically called.
Reference:-
http://www.oodesign.com/dependency-inversion-principle.html











Comments

Post a Comment

Popular posts from this blog

Draw Over Screen App Example Android

Image
We always interact with some app which are drawn over screen. Facebook Messenger is one of the good example of that. When you receive a new message it pops up over screen even if Messenger App is closed. So how to achieve this. This required very basic setup in your application. We are taking  targetSdkVersion 21  in build.gradle to avoid Runtime Permission implementation of SDK 23. Step 1 :- Give permission in your manifest file i.e. android.permission.SYSTEM_ALERT_WINDOW < uses-permission android :name= "android.permission.SYSTEM_ALERT_WINDOW" /> Step 2:- Then you have create your layout for overdraw window We are showing a button <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android= "http://schemas.android.com/apk/res/android" android:orientation= "vertical" android:layout_width= "match_parent" android:layout_height= "wrap_content" android:grav
Read more

Sync Adapter Overview

Sync Adapter, as its name it is use to sync device data with server data. This sync can be done on following conditions:- When server data is changed. When device data is changed. At regular interval or specific time. On demand, such as user action. First lets understand SyncAapter Framework. Sync Adapter framework has 4 basic components :- Stub Authenticator. (For accessing account information.) Stub Content Provider (Used when your data is other than SQL) Syn Adapter (Entire Class runs in background thread. You on't need to create your own.) Binder Service (This allow sync adapter framework to call authenticator method.) Note:- Sync Adapter is not only used to sync SQL data, you can sync files, text, and other kind of data with sync adapter but for that need to use Stub Content Provider. Stub Authenticator  Now segregate all the information and come to the flow. So when request Sync. Binder service runs and called onPerformSync after authenticati
Read more

Launch Stock Apps using Intent

Some time we have to launch stock applications in our android phone without need of performing some action. Like Email, Browser,Calculator,Calendar, Contacts, Gallery, Market and so on. This can be done by using power full function  makeMainSelectorActivity()  method   of Intent class. Syntax is pretty simple, just to write few lines of code Say you want to open email app. Intent intent= Intent . makeMainSelectorActivity ( Intent . ACTION_MAIN , Intent . CATEGORY_APP_EMAIL ); startActivity(intent); For other apps you just have to replace second parameter i.e. category. Here is some app listed category from android developer refernce CATEGORY_APP_BROWSER Used with  ACTION_MAIN  to launch the browser application. CATEGORY_APP_CALCULATOR Used with  ACTION_MAIN  to launch the calculator application. CATEGORY_APP_CALENDAR Used with  ACTION_MAIN  to launch the calendar application. CATEGORY_APP_CONTACTS Used with  ACTION_MAIN  to launch the contacts application
Read more