Classes / Objects / Methods

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Classes / Objects / Methods

• Chapter 4

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Object Oriented Programming

• Divides a program into Modules/Classes
• Uses Classes and Objects to simulate real world
  environments
• Basic Programming Components
• Classes
• Objects
• Methods

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Class

• Specifies the definition of a particular kind of
  object
• Frog
• Snowman
• Cell phone
• Blueprint / design for how to create an object of
  that type
• Class names begin with a Capital letter

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Class

• Properties
• Characteristics
• Methods
• Behaviors

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Objects

• Specific Instances of a Class
• Implementation of the Class Definition
• Spot ? one specific dog
• Frosty ? one specific snowman
• All specific objects of the same class share the
  same definition
• Same Properties can be modified
• Same Methods can be modified
• Object names begin with lowercase letter

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Dog Object

• All Instances of Class Dog Have
• Properties
• Name
• Breed
• Weight
• Color
• Methods
• Walk
• Bark
• Jump

• Each Instance Has
• Properties
• Spot
• Mutt
• 10 pounds
• Black
• Methods
• Walk
• Bark
• Jump
• (can be modified to fit Spots requirements)

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Methods

• Sequence of Instructions
• Tasks that can be performed
• Some are predefined within the Class
• Dog has a bark method
• Others are Created or Modified
• Methods organize the program
• Divide the program into manageable pieces

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Parameters

• Pieces of Information that need to be sent to the
  Method
• Turn Toward (what)
• Turn Toward Snowwoman

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Levels of Methods

• Global Methods (World Level)
• Methods that reference more than one object
• Class Methods
• Methods that define a behavior for one single
  object

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Create New Method

• Snowpeople (problem 4-1)
• flipsHat
• Raises right arm
• Grabs Hat
• Tips toward snowwoman
• Returns Hat to Head
• World Method
• Uses snowman and snowwomen
• World
• Method
• Create New Method
• Name ? flipsHat

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Add Method Instructions
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Calling a Method

• New Method must be Called
• Program Instructions must indicate to Execute the
  new Method
• In Alice
• Drag Method into World.MyFirstMethod
• In Other Languages
• Call the Method using Method Name

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Parameters

• Allows communication with Methods
• Communicate Values (Numbers, Colors)
• Communicate Object Names

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Create Method with Parameter

• Create Method called dance
• Object will jump up and down and spin around
• Create Parameters
• Parameter 1
• Which object to dance
• Parameter 2
• How many times to Spin

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Creating Parameter

• Which object to Dance
• Name
• Arbitrary
• Placeholder holds place of the actual object
  the will be used in the method
• Type
• Number
• Boolean (True/False)
• Object
• Other (Sound, Color, Etc.)

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Parameter

• Parameters show in Upper Left of Method Panel
• When Method is Called (Used)
• Object must be sent as an Argument to Method

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Use Parameter in Method
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Calling Method with Parameter

• When using Method you must include Parameter
• Use dance method after flipHat
• Example 1 Requires an object to dance

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Multiple Parameters

• Add Second Parameter How many times to Spin
• Name numberToSpin
• Type Number
• Use in the Turn Instruction

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Modify Method Call

• Change 2nd Parameter
• Pick any 2 different numbers

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Create Another Method

• Create a Method for Snowman Blinking His Eyes
• Is this a World / Global Method
• Is this a Class Method
• Why
• How is it Created?

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Homework

• Chapter 4, Section 1 (4-1)
• 3 Gallop and Jump
• 4 Helicopter Flight
• Chapter 4, Section 2 (4-2)
• 6 Frog Escape

Bring electronic copy of homework to class Bring
printed copy of homework to submit
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Class Methods

• Class Methods are methods that define a behavior
  for one single class object.
• Select Horse Object
• Methods
• Create New Method
• gallop

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Guidelines for Class Methods

• Create lots of class methods as necessary
• Do not call world-level methods from within a
  class-level method
• Do not use instructions for other objects from
  within a class-level method
• You can use parameters to send necessary
  information instead of referring to other
  specific objects from within the method.

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Inheritance

• Creating a class on a previously defined class
• Adding functionality to existing class by
  defining new methods or editing existing ones
• Different members of design team can work on
  different methods for the class

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Creating a New Class in ALICE

• Save object with new class methods as a New Class
• Code Reuse
• Galloping Horse
• 2 Step Process
• Rename existing object in Object Tree
• Save As a New Class

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Rename Object

• Select the Object in the Object Tree
• Right-Click
• Rename
• Select a New Meaningful Name for Object
• GallopingHorse

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Save As New Class

• Select the Object in
• the Object Tree
• Right-Click
• Save Object
• Navigate to folder
• where you want to save the object
• Other objects Alice\Alice\Required\Gallery
• .a2c extension ? Alice 2.0 class

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New Class

• New Class (GallopingHorse) is now available in
  Object Gallery
• All objects of GallopingHorse
• all methods of horse
• class-method gallop

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Homework

• Exercise 4-3
• 10
• 11 ? use a say instruction not a sound file so
  all worlds dont have to import sound file
• Bring electronic copy of homework to class
• Bring printed copy of homework to submit