controller

Apr 10, 2023 Controller - K.INIYA CSE Prefinal Year

CONTROLLER

1

OBJECT ORIENTED

ANALYSIS AND DESIGN

Apr 10, 2023 Controller - K.INIYA CSE Prefinal Year 2

DEFINITION

It is the first object beyond the UI Layer responsible for receiving or handling a system operation message.

The controller pattern assigns the responsibility of dealing with system events to a non class that represents the overall system or a use case scenario.


PROBLEM

What first object beyond the UI layer receives and coordinates a system operation?


SOLUTION

Assigning the responsibility to a class representing one of the following option

1)representing the overall system a root object, a device that the software is running within or a major subsystem. These are the variations of facade controller.


CONTD.,

2)Represents a Use Case Scenario

within which the system event occurs, often named

<usecaseName> Handler, <usecaseName> Coordinator, or <usecaseName> Session.


CONTD.,

(a) Use the same controller class for all system events in the same usecase scenario.

(b) Informally, a session is an instance of a conversion with an actor. Sessions can be of any length but are often organized in terms of usecases (use case Sessions).


EXAMPLE

Some System Operations of NextGen Pos Application

endsale()enterItem()makeNewSale()makePayment() …………………….

System


ItemID

Quantity

ENTER SAVE

:SaleJFrame

:?????

actionPerformed (actionEvent)

enterItem(itemID,qty)

UI Layer

Domain Layer

Presses Button

System Operation Messages

Which class of object should be responsible for receiving system event message?

Controller


ItemID

Quantity

ENTER SAVE

:SaleJFrame

:Register


UI Layer

Domain Layer

Presses Button

enterItem(itemID,qty)

System Operation Messages

Controller

:Sale

1:makeLineitem(itemID,qty)

Desirable Coupling of UI to domain Layer

Apr 10, 2023 Controller - K.INIYA CSE Prefinal Year

ItemID

Quantity

ENTER SAVE

:SaleJFrame

:Sale


UI Layer

Domain Layer

Presses Button

Sale Jframe should not send this message

10

1:makeLineitem(itemID,qty)

Less Desirable Coupling of User Interface to domain Layer


CONTROLLER CHOICES IN TERMS OF INTERACTION DIAGRAM

:Register

:ProcessSaleHandler

enterItem(id,quantity)

enterItem(id,quantity)


System Operations Discovered during system

behaviour analysis

Allocation of system operations during design

using one façade controller

endsale()enterItem()makeNewSale()makePayment()makeNewReturn()enterReturnItem() …………………….

System

endsale()enterItem()makeNewSale()makePayment()makeNewReturn()enterReturnItem() …………………….

Register……………………………….


DISCUSSION

UI Layer does not contain Application Logic rather UI Layer Objects must delegate work requests to another layer.System receives external input events ,that involves GUI operated by a Person.

1) Other inputs are external messages.2) For example: in a call processing

telecommunications switch or signals from sensors.


CONTD.,

A controller then suffers from bad (low) cohesion violating the principle of High Cohesion. Facade controller are suitable when there are “too many” system events, or when the User Interface (UI) cannot redirect system event messages to alternating controllers, such as in a message processing system.


CONTD.,

Boundary, Entity, Control classes in UP. (a)Boundary objects are abstractions of the

interfaces. (b)Entity objects are the application

independent domain software objects. (c)Control objects are use Case handlers as in

Controller Pattern.


BENEFITS

Increased potential for reuse and pluggable interfaces.

Opportunity to reason about the state of the usecase.


RELATED PATTERNS

Command- In a message handling system, each message may be represented and handled by a separate command object.Façade- A façade controller is a kind façade.Layers- Placing domain logic in the domain Layer rather than the Presentation Layer is the part of the Layers.


CONTD.,

• Pure Fabrication- A use case Controller is a kind of Pure Fabrication.

(Pure Fabrication is a class that does not represent a concept in the problem Domain, specially made up to achieve low coupling, high cohesion and reuse potential)


IMPLEMENTATION

Java Technologies are used for implementation for the two reasons:

i. Rich Client in Java Swing.ii. Web UI with struts on the Server.


RICH CLIENT UIPackage.com.craiglarman.nextgen.ui.swing;Public class ProcessSaleJFrame extends Jframe{Private Register register;Public ProcessSaleJFrame(Register_register){register=_register;}Private Jbutton BTN_ENTER_ITEM()Private Jbutton getBTN_ENTER_ITEM(){If (BTN_ENTER_ITEM!=null)return BTN_ENTER_ITEM;else


BTN_ENTER_ITEM=new Jbutton();BTN_ENTER_ITEM.setText(“ENTER”)BTN_ENTER_ITEM.addActionListener(newActionListener(){Public void actionPerformed(ActionEvent e){ItemID id=Transformer.toItemID(getTXT_ID().getText());Int qty=Transformer.toInt(getTXT_QTY().getText());register.enterItem(id,qty);}});return BTN_ENTER_ITEM;}}


BLOATED CONTROLLERS

DEFINITIONPoorly designed, a controller class with have

low cohesion-unfocused and handling too many areas of responsibility, this is called a

Bloated Controller.


SIGNS OF BLOATING

There is only a Single Controller class receiving all system events in the system. This sometimes happens if a façade controller is chosen.The Controller itself performs many of the tasks necessary to fulfill the system event. This usually involves a violation of Information Expert and High Cohesion.


CONTD.,

A Controller has many attributes and it maintains significant information about the system or domain, which should have been distributed to other objects, or it duplicates information found elsewhere.


Among the cures for a bloated controller are these two:

1)Add more controllers- a system does not have to need only one. For example:

consider the application with many system events, such as an Airline Reservation System.


It may contain the following Controllers

2) Design the controller so that it primarily delegates the fulfillment of each system operation responsibility to other objects.

Use Case Controllers

Make Reservation Handler

Make Schedules Handler

Make Fares Handler


THANK YOU

controller

Education

system controller

controller class

domain layer controller

quantity controller

faade controller

controller pattern

use case controller

system events