Classes / Objects / Classes / Objects / MethodsMethods

Chapter 4Chapter 4

Object Oriented ProgrammingObject Oriented Programming

Divides a program into Divides a program into Modules/ClassesModules/Classes

Uses Classes and Objects to simulate Uses Classes and Objects to simulate real world environmentsreal world environments

Basic Programming ComponentsBasic Programming Components• ClassesClasses• ObjectsObjects• MethodsMethods

ClassClass

Specifies the definition of a particular Specifies the definition of a particular kind of objectkind of object• FrogFrog• SnowmanSnowman• Cell phoneCell phone

Blueprint / design for how to create Blueprint / design for how to create an object of that typean object of that type

Class names begin with a Capital Class names begin with a Capital letterletter

ClassClass

PropertiesProperties• CharacteristicsCharacteristics

MethodsMethods• BehaviorsBehaviors

ObjectsObjects

Specific Instances of a ClassSpecific Instances of a Class Implementation of the Class DefinitionImplementation of the Class Definition

• Spot Spot one specific dog one specific dog• Frosty Frosty one specific snowman one specific snowman

All specific objects of the same class share All specific objects of the same class share the same definitionthe same definition• Same Properties – can be modifiedSame Properties – can be modified• Same Methods – can be modifiedSame Methods – can be modified

Object names begin with lowercase letterObject names begin with lowercase letter

Dog ObjectDog Object All Instances of Class All Instances of Class

Dog HaveDog Have• PropertiesProperties

NameName

BreedBreed WeightWeight ColorColor

• MethodsMethods WalkWalk BarkBark JumpJump

Each Instance HasEach Instance Has

• PropertiesProperties SpotSpot MuttMutt 10 pounds10 pounds BlackBlack

• MethodsMethods WalkWalk BarkBark JumpJump(can be modified to fit (can be modified to fit

Spot’s requirements)Spot’s requirements)

MethodsMethods

Sequence of InstructionsSequence of Instructions Tasks that can be performedTasks that can be performed Some are predefined within the ClassSome are predefined within the Class

• Dog has a bark methodDog has a bark method Others are Created or ModifiedOthers are Created or Modified Methods organize the programMethods organize the program

• Divide the program into manageable Divide the program into manageable piecespieces

ParametersParameters

Pieces of Information that need to be Pieces of Information that need to be sent to the Method sent to the Method

Turn Toward (what)Turn Toward (what) Turn Toward SnowwomanTurn Toward Snowwoman

Levels of MethodsLevels of Methods

Global Methods (World Level)Global Methods (World Level)• Methods that reference more than one Methods that reference more than one

objectobject Class MethodsClass Methods

• Methods that define a behavior for one Methods that define a behavior for one single objectsingle object

Create New MethodCreate New Method Snowpeople (problem 4-1)Snowpeople (problem 4-1)

• flipsHatflipsHat Raises right armRaises right arm Grabs HatGrabs Hat Tips toward snowwomanTips toward snowwoman Returns Hat to HeadReturns Hat to Head

World Method World Method • Uses snowman and snowwomenUses snowman and snowwomen• WorldWorld• MethodMethod• Create New MethodCreate New Method• Name Name flipsHat flipsHat

Add Method InstructionsAdd Method Instructions

Calling a MethodCalling a Method

New Method must be “Called”New Method must be “Called” Program Instructions must indicate to Program Instructions must indicate to

Execute the new MethodExecute the new Method In AliceIn Alice

• Drag Method into World.MyFirstMethodDrag Method into World.MyFirstMethod In Other LanguagesIn Other Languages

• Call the Method using Method NameCall the Method using Method Name

ParametersParameters

Allows communication with MethodsAllows communication with Methods

• Communicate Values (Numbers, Colors)Communicate Values (Numbers, Colors)

• Communicate Object NamesCommunicate Object Names

Create Method with ParameterCreate Method with Parameter

Create Method called “dance”Create Method called “dance”• Object will jump up and down and spin aroundObject will jump up and down and spin around

Create ParametersCreate Parameters• Parameter 1Parameter 1

Which object to danceWhich object to dance

• Parameter 2Parameter 2 How many times to SpinHow many times to Spin

Creating ParameterCreating Parameter

Which object to DanceWhich object to Dance• NameName

Arbitrary Arbitrary Placeholder – holds place of the actual Placeholder – holds place of the actual

object the will be used in the method object the will be used in the method

• Type:Type: NumberNumber Boolean (True/False)Boolean (True/False) ObjectObject Other (Sound, Color, Etc.)Other (Sound, Color, Etc.)

ParameterParameter

Parameters show in Upper Left of Method Parameters show in Upper Left of Method PanelPanel

When Method is Called (Used)When Method is Called (Used)• Object must be sent as an Argument to Method Object must be sent as an Argument to Method

Use Parameter in MethodUse Parameter in Method

Calling Method with ParameterCalling Method with Parameter

When using Method you must include When using Method you must include ParameterParameter

Use dance method after flipHatUse dance method after flipHat Example 1: Requires an object to Example 1: Requires an object to

dancedance

Multiple ParametersMultiple Parameters

Add Second Parameter – How many Add Second Parameter – How many times to Spintimes to Spin• Name: numberToSpinName: numberToSpin• Type: NumberType: Number• Use in the Turn InstructionUse in the Turn Instruction

Modify Method CallModify Method Call

Change 2Change 2ndnd Parameter Parameter Pick any 2 different numbersPick any 2 different numbers

Create Another MethodCreate Another Method

Create a Method for Snowman Create a Method for Snowman Blinking His EyesBlinking His Eyes• Is this a World / Global MethodIs this a World / Global Method• Is this a Class MethodIs this a Class Method

WhyWhy How is it Created?How is it Created?

HomeworkHomework

Chapter 4, Section 1 (4-1)Chapter 4, Section 1 (4-1)• #3 – Gallop and Jump#3 – Gallop and Jump• #4 – Helicopter Flight#4 – Helicopter Flight

Chapter 4, Section 2 (4-2)Chapter 4, Section 2 (4-2)• #6 – Frog Escape#6 – Frog Escape

Bring electronic copy of homework to classBring electronic copy of homework to classBring printed copy of homework to submitBring printed copy of homework to submit

Class MethodsClass Methods

Class Methods are methods Class Methods are methods that define a behavior for one that define a behavior for one single class object.single class object.

Select Horse ObjectSelect Horse Object MethodsMethods Create New MethodCreate New Method gallopgallop

Guidelines for Class MethodsGuidelines for Class Methods

Create lots of class methods as necessaryCreate lots of class methods as necessary Do not call world-level methods from Do not call world-level methods from

within a class-level methodwithin a class-level method Do not use instructions for other objects Do not use instructions for other objects

from within a class-level methodfrom within a class-level method You can use parameters to send necessary You can use parameters to send necessary

information instead of referring to other information instead of referring to other specific objects from within the method.specific objects from within the method.

InheritanceInheritance

Creating a class on a previously Creating a class on a previously defined classdefined class

Adding functionality to existing class Adding functionality to existing class by defining new methods or editing by defining new methods or editing existing onesexisting ones

Different members of design team Different members of design team can work on different methods for can work on different methods for the classthe class

Creating a New Class in ALICECreating a New Class in ALICE

Save object with new class methods Save object with new class methods as a New Classas a New Class• Code ReuseCode Reuse• Galloping HorseGalloping Horse

2 Step Process2 Step Process• Rename existing object in Object TreeRename existing object in Object Tree• Save As a New ClassSave As a New Class

Rename ObjectRename Object

Select the Object in the Select the Object in the Object TreeObject Tree

Right-ClickRight-Click RenameRename Select a New Meaningful Select a New Meaningful

Name for ObjectName for Object• GallopingHorseGallopingHorse

Save As New ClassSave As New Class

Select the Object in Select the Object in

the Object Treethe Object Tree Right-ClickRight-Click Save ObjectSave Object Navigate to folder Navigate to folder

where you want to save the objectwhere you want to save the object

Other objects: Alice\Alice\Required\GalleryOther objects: Alice\Alice\Required\Gallery

.a2c extension .a2c extension Alice 2.0 class Alice 2.0 class

New ClassNew Class

New Class (GallopingHorse) is now New Class (GallopingHorse) is now available in Object Galleryavailable in Object Gallery

All objects of GallopingHorse All objects of GallopingHorse • all methods of horse all methods of horse • class-method gallopclass-method gallop

HomeworkHomework

Exercise 4-3 Exercise 4-3 • #10#10• #11 #11 use a say instruction not a sound use a say instruction not a sound

file so all worlds don’t have to import file so all worlds don’t have to import sound filesound file

• Bring electronic copy of homework to classBring electronic copy of homework to class• Bring printed copy of homework to submitBring printed copy of homework to submit