7/30/2019 Lecture 9 Objects and Classes 3

1/27

CMSC22OOP

ObjectsandClasses3

HappyNewYearJ

7/30/2019 Lecture 9 Objects and Classes 3

2/27

Objec:ves

ReviewofObjectsandClasses ClassMembers

Instancevariables/methodsClassvariables/methods

TypesofClasses ClassesonotherOOPLs.

7/30/2019 Lecture 9 Objects and Classes 3

3/27

ReviewClasses

Classesdefinetheproper:esandbehaviors(methods)objectsthatbelongtoithave.

AClassisastructurecomposedofAributes(instanceandclassvariablesMethods/Opera:onthatmanipulatethedata(instanceandclassmethods)

7/30/2019 Lecture 9 Objects and Classes 3

4/27

publicclassCar{

Stringcolor;

Stringplatenumber;intspeed;

//constructorwithparametersforini2aliza2on

publicCar(Stringnplatenumber,Stringncolor){

platenumber=nplatenumber; color=ncolor;

}

publicvoidstop()

{ speed=0;

}

}

7/30/2019 Lecture 9 Objects and Classes 3

5/27

publicclassCarExample{

publicsta:cvoidmain(Stringargs[]){

//passtheparameterstotheconstructor

Carcar1=newCar(XYZ123,RED);

Carcar2=newCar(ABC456,GREEN);

}

}

UsingConstructorswith

Parameters

7/30/2019 Lecture 9 Objects and Classes 3

6/27

Car

Stringplatenumber;

Stringcolor;

intspeed;

stop()

accelerate(int)

repaint(String)

Car.javaProgram

car1

platenumber:XYZ13

color:Red

speed:0

stop()

accelerate(int)

repaint(String)

car1

platenumber:ABC456

color:Green

speed:0

stop()

accelerate(int)

repaint(String)

7/30/2019 Lecture 9 Objects and Classes 3

7/27

Addi:onalTerms

Instancearibute/variableAributespecifictoaninstance/object.Eachobjectoftheclasshavethesamesetofproper:esBUTmayhavedifferentvaluesforeachproperty.

Instancemethod/opera:onMethodwheretheresultofwhichisdependentonthecurrentstateoftheobjectinques:on.

7/30/2019 Lecture 9 Objects and Classes 3

8/27

DeclaringanInstanceVariable/

InstanceMethod

publicclassCar{

Stringcolor;

Stringplatenumber;

intspeed;

publicvoidstop(){

speed=0;

}

}

//InstanceVariables

//InstanceMethods

7/30/2019 Lecture 9 Objects and Classes 3

9/27

Car

Stringplatenumber;Stringcolor;

intspeed;

stop()

Car.javaProgram

car1

platenumber:XYZ13

color:Red

speed:0

stop()

car1

platenumber:ABC456

color:Green

speed:0

stop()

7/30/2019 Lecture 9 Objects and Classes 3

10/27

Accessinginstanceaributesand

methodsofanobject(JavaStyle)

InstanceAributes.;Ex.car1.color;

InstanceMethodInvoca:on.();Ex.car1.stop();

7/30/2019 Lecture 9 Objects and Classes 3

11/27

Addi:onalTerms

Classaribute/variableAributethatiscommonto/reflectedinallobjectsintheclass.

I.e.Global(butnotexactly). Classmethod/opera:on

MethodthatiscommontoallobjectsoftheclassandthattheresultofwhichisNOT:edtoany

par:cularinstanceoftheclass.

7/30/2019 Lecture 9 Objects and Classes 3

12/27

DeclaringanInstanceVariable/

InstanceMethod

publicclassCar{

Stringcolor;

Stringplatenumber;

intspeed;

sta2cintnumberOfCars;

publicsta2cintgetNumberOfCars(){

returnnumberOfCars;

}

}

//ClassVariable

//ClassMethod

7/30/2019 Lecture 9 Objects and Classes 3

13/27

Car

Stringplatenumber;Stringcolor;

intspeed;

IntnumberOfCars;

stop()

getNumberOfCars()

Car.javaProgram

car1

platenumber:XYZ13

color:Red

speed:0

stop()

car1

platenumber:ABC456

color:Green

speed:0

stop()

7/30/2019 Lecture 9 Objects and Classes 3

14/27

Accessingclassaributesand

methodsofanobject(JavaStyle)

ClassAributes.;Ex.Car.numberOfCars;

ClassMethodInvoca:on.();Ex.Car.getNumberOfCars();

7/30/2019 Lecture 9 Objects and Classes 3

15/27

Also

Instancemethodscanaccessinstancevariablesandinstancemethodsdirectly.

Instancemethodscanaccessclassvariablesandclassmethodsdirectly.

Classmethodscanaccessclassvariablesandclassmethodsdirectly.

Classmethods

cannot

accessinstancevariablesorinstancemethodsdirectly

7/30/2019 Lecture 9 Objects and Classes 3

16/27

NoteonDestructors

DestructorsSpecializedmethodsthatdeallocatememory.Maybeimplicitlyorexplicitlycalled(i.e.inC++)Javadoesnthavedestructorsbecauseofitsautogarbagecollec:onfeatures.

7/30/2019 Lecture 9 Objects and Classes 3

17/27

Note

ReusabilityUsefulnessoftheclass/objectsinmorethanoneobject.

7/30/2019 Lecture 9 Objects and Classes 3

18/27

TypesofClasses

En2tyClasses/DataClassesClasseswhoseobjectsencapsulatethedatausedinasystem

Data-relatedobjects.E.g.String,Student,Car

7/30/2019 Lecture 9 Objects and Classes 3

19/27

TypesofClasses

U2lityClassesClassesthatmaintainu:litymethodsandusuallyarenotinstan:atable

java.lang.Math

7/30/2019 Lecture 9 Objects and Classes 3

20/27

TypesofClasses

SingletonObjects{Class}Objectwheninstan:ated,nootherobjectofthesameclassexistsinthegivencontext.

E.g.java.lang.System

7/30/2019 Lecture 9 Objects and Classes 3

21/27

TypesofClasses

ControlClasses,View(Interface)ClassesControlClassesforLogicViewClassesfortheUserInterface

7/30/2019 Lecture 9 Objects and Classes 3

22/27

CLASSESONOTHERPROGRAMMINGLANGUAGES

7/30/2019 Lecture 9 Objects and Classes 3

23/27

7/30/2019 Lecture 9 Objects and Classes 3

24/27

7/30/2019 Lecture 9 Objects and Classes 3

25/27

7/30/2019 Lecture 9 Objects and Classes 3

26/27

CreateaClass

Fourinstancevariables Twoclassvariables Threeinstancemethods Oneclassmethod

7/30/2019 Lecture 9 Objects and Classes 3

27/27

SummarySomeques:ons?

Whatisaclass? Whatisanobject? Whatisabstrac:on? Whatarethemembersofaclass? Whatisthedifferencebetweenaninstancemethod/variableandaclassmethod/variable?

Whatareconstructors/destructors?