MELJUN CORTES JEDI Slides-5.3 Implementing Controllers

7/29/2019 MELJUN CORTES JEDI Slides-5.3 Implementing Controllers

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Software Engineering 1The use of the slide has prior approval from the orignal author (Ms. Florence Balagtas) from the JEDI Introduction to Programming I Course Materials.

Implementation

ImplementingControllers

TOPIC THREE


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Controllers

Controllers are responsible for the implementation of thebehavior or functional requirements of the system.

Implementing controllers is similar to writing codes in other

programming language courses. It is better to implement controllers using abstract classes

and interface.

NOTE: The following slides is a basic review on abstractclasses and interfaces which came from the JEDIIntroduction to Programming I.


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Abstract Classes

Abstract class

a class that cannot be instantiated.

often appears at the top of an object-oriented programming classhierarchy, defining the broad types of actions possible with objectsof all subclasses of the class.


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Abstract Classes

abstract methods

methods in the abstract classes that do not have implementation

To create an abstract method, just write the method declarationwithout the body and use the abstract keyword

For example,


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Sample Abstract Classpbli Sys em. u.prin ln( Lving hin ating .." ;}/***abstractmethodwalk*Ww atth is et hdtob eov erdd en ysbla ss eo f*Liv nTig*/pub iabstratvoidwalk()}


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Abstract Classes

When a class extends the LivingThing abstract class, it isrequired to override the abstract method walk(), or else, thatsubclass will also become an abstract class, and thereforecannot be instantiated.

For example,p bicvo dwak({ S sem.ou .ritl("Hmn walks. .");}}


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Coding Guidelines

Use abstract classes to define broad types of behaviors atthe top of an object-oriented programming class hierarchy,and use its subclasses to provide implementation details ofthe abstract class.


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Interfaces

An interface

is a special kind of block containing method signatures (and possiblyconstants) only.

defines the signatures of a set of methods, without the body.

defines a standard and public way of specifying the behavior ofclasses.

allows classes, regardless of their locations in the class hierarchy, toimplement common behaviors.

NOTE: interfaces exhibit polymorphism as well, since program maycall an interface method, and the proper version of that method willbe executed depending on the type of object passed to the interfacemethod call.


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Why do we use Interfaces?

To have unrelated classes implement similar methods

Example:

Class Line and MyInteger

Not related Both implements comparison methods

isGreater isLess

isEqual


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Why do we use Interfaces?

To reveal an object's programming interface withoutrevealing its class

To model multiple inheritance which allows a class to havemore than one superclass


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Interface vs. Abstract Class

Interface methods have no body

An interface can only define constants

Interfaces have no direct inherited relationship with anyparticular class, they are defined independently


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Interface vs. Class

Common:

Interfaces and classes are both types

This means that an interface can be used in places where a classcan be used

For example:PersonInterfacepi = new Person();Prson p=newPerson()

Difference:

You cannot create an instance from an interface

For example:P ro nI trace p ne eson In efce( );//E RR!


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Interface vs. Class

Common:

Interface and Class can both define methods

Difference: Interface does not have any implementation of the methods


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Creating Interfaces

To create an interface, we write:

public interface [InterfaceName] {

//some methods without the body}


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Creating Interfaces

As an example, let's create an interface that definesrelationships between two objects according to the naturalorder of the objects.

pblicinterface elation{ pblicol asGrae(Objecta,Ob jectb);pblicol asLesbecta,Objec tb);pblicol asEqa(Ojecta,Obje ctb);}


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Creating Interfaces To use an interface, we use the implements keyword.

For example,* Tilseieiesge*p b

p riat edoub l x 1;p riat edoub l x 2;p riat edoub l y 1;p riat edoub l y 2;

p ubl i c Li ne( do u ble x1, d ou b le x2,d

this.x 1=x;this.x 2=x;this.y1 =y;this.y2 =y;

}


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Creating Interfaces


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Creating Interfaces

When your class tries to implement an interface, alwaysmake sure that you implement all the methods of thatinterface, or else, you would encounter this error,

L ne.java:4: Line is no t abstract and does not override abstractpbcsLi eime entRen1e


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Relationship of an Interface

to a Class A class can only EXTEND ONE super class, but it canIMPLEMENT MANY interfaces.

For example:

public class Person imple ments PersonInterface,LivingThi ngWhateverI ter ae {//someco de hr}


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Relationship of an Interface

to a Class Another example:public class ComputerScie nceStudent extends Student ip en ers nIntf ce, Liv//somecode hr}


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Inheritance among Interfaces

Interfaces are not part of the class hierarchy. However,interfaces can have inheritance relationship amongthemselves

For example:

p ...}


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Summary

Controllers

Review on Abstract Classes and Interfaces

Documents

MELJUN CORTES JEDI Slides-5.3 Implementing Controllers