Building Multitier Programs with Classes

Creating Properties in a Class • Declare all variables in a class as privateencapsulation • private variable values are only available to procedures in the class • When objects are crea

Week 9 Building Multitier Programs with

Classes

2- 2

Contents

• 1 Review to OOP

– Create properties – Create methods

• 2 3-tier application

• 3.Example

• 4 Exercises

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1 Creating Properties in a Class

• Declare all variables in a class as private(encapsulation)

• private variable values are only

available to procedures in the class

• When objects are created from a class,

values must be assigned values and values must be passed from the class

Creating Classes

A Read-Only Property

class Myclass

{

private int myVar=0;

public int MyProperty {

get { return myVar; } }

}

class Myclass

{

private int myVar=0;

public int MyProperty {

get { return myVar; } }

}

Creating Classes

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Constructors

•

• initializes an object when created

• Same name as its class

• similar to a method

• have no explicit return type

A constructor is a method that

automatically executes when an

object is instantiated.

A constructor is a method that

automatically executes when an

object is instantiated.

Creating Classes

Constructors with parameters

• for some situations, we need a

constructor that accepts parameters

• Parameters are added to a constructor in the same way that they are added to a

method

Creating Classes

Two methods have the same name but a different list of arguments

A signature is the argument list of a method or procedure

A signature is the argument list of a method or procedure

Creating Classes

Retrieving shared Variables

• When placed on a static keyword, the

keyword makes values accessible without instantiating the object of the class

class Myclass

{

private static int myVar=0;

public static int MyProperty

{ get { return myVar; } }

}

class Myclass

{

private static int myVar=0;

public static int MyProperty

{ get { return myVar; } }

}

Creating Classes

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Create method

• Subroutines

Throwing and Catching

• You can make an exception

• Use the try/catch block to enclose code that could cause an exception

– Exampe

Creating Classes

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3-tier application

• What is 3-tier model?

• Physical & logic model

• What is business tier

• Business object & original object

• Sending message between tier-s

2 What is 3-tier model?

• “Plug-in” new components

Applications designed in components (services) where each section performs part of the necessary actions.

Applications designed in components (services) where each section performs part of the necessary actions.

Object-Oriented Programming

Business Object Validation Calculations Business logic Business rules

User Services

What is 3-tier model?

Multitier Applications

• Presentation tier
the user interface

You can change the method of delivery without changing the processing

You can change the method of delivery without changing the processing

What is 3-tier model? More detail

• presents information to the user, and

collects user input

What is 3-tier model?

UI

• logic to decide what the user sees, the

navigation paths, and how to interpret user input

• accepts user input and then provides it to the business logic, where it can be

validated, processed

• In NET, UI code is almost event-driven

• Only request to middle-tier

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What is 3-tier model?

Business logic

• Definition from Microsoft

"The combination of validation edits, logon verifications, database lookups, policies, and algorithmic

transformations that constitute an enterprise's way of doing business".

• must reside in a separate tier from the UI code

• Request to DAL

What is 3-tier model?

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What is 3-tier model?

Data storage and management

• Database servers such as SQL Server or MS Acccess, Oracle

• physical creation, retrieval, update, and

deletion of data

Physical & logic model Framework Design

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3-tier in logic and physical

UI Win.app

UI

Middle-tier VB6, VB.Net, C#, Java

Data –tier (DAL) VB6, VB.Net, C#, Java

Data store

Server 1

Data store Server 3 Data store

Server 2

Physical & logic model

Single tier System

• Good for standalone environments,

• install everything on a single client

workstation

• n-tier systems can run on a single machine

Physical & logic model 3-tier

• can centralize all access to the

database on a single machine

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Business objects and Object

• Object: encapsulate, abstract entity or

Why using Business tier?

• Cannot assume that incoming data is valid

• Not all incoming data is from the user

• Data from the database may also be invalid

– Translated data

– Updates to data from other applications

– Errors ???

+Can not raise message in middle, data tier

+Can not generate SQL command in middle, UI tier

Example

• Hanoi tower

– Using event for message sending from business tier to UI.

• Contact phone application

– Using 2 data store: SIM & PHONE

– Using exception

• Using Class Library (Class_Library.PPT)

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3.Class Library

Make library for others projrct

Menu File->All new Project->Class Library From main project->Add Refference

Example

How to make a 3-tier app