1. Classes / Objects / Methods
Chapter 4

2. Object Oriented Programming
Divides a program into Modules/Classes
Uses Classes and Objects to simulate real world environments
Basic Programming Components
Classes
Objects
Methods

3. 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
Alice objects are 3-D models.

4. Class
Properties
Characteristics
Methods
Behaviors

5. 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 Ob

6. Dog Object All Instances of Class Dog Have Each Instance Has
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 Spot’s requirements)

7. 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

8. Parameters Pieces of Information that need to be sent to the Method
Turn Toward (what)
Turn Toward Snowwoman
Methods are like a series of instructions  Recipe
Parameters are the Specifics for that Recipe  how much water to add

9. Levels of Methods Global Methods (World Level) Class Methods
Methods that reference more than one object
Class Methods
Methods that define a behavior for one single object

10. Create New Method Snowpeople (problem 4-1) World Method 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
Modify your object

12. Add Method Instructions

13. 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
The program starts running with the MyFirstMethod code.

15. Parameters Allows communication with Methods
Communicate Values (Numbers, Colors)
Communicate Object Names

16. 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

17. Creating Parameter Which object to Dance Name Type: 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.)
1st parameter  which object to Dance
Name: snowperson
Type: object

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

19. Use Parameter in Method
Drag the parameter into the method code section (as you would any other object)

20. Calling Method with Parameter
When using Method you must include Parameter
Use dance method after flipHat
Example 1: Requires an object to dance
Put after flipsHat – Use with Snowman and Snowwoman

21. Multiple Parameters Add Second Parameter – How many times to Spin
Name: numberToSpin
Type: Number
Use in the Turn Instruction

22. Modify Method Call Change 2nd Parameter Pick any 2 different numbers
Run the program using the method with parameters.

23. 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?

24. Homework Chapter 4, Section 1 (4-1) Chapter 4, Section 2 (4-2)
#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

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

26. 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.
Create lots of class methods, they are useful and helpful  code reuse
Do not call world-level methods  you may use an object of this class in another world that does not have this world-level method (error)
Class-level methods should only refer to objects of the class that the method was created for. You may use this objects of this class and this class-level methods in other worlds and other programs that do not have these other objects.

27. 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

28. 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

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

30. 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

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

32. Homework
Exercise 4-3
#10
#11  use a say instruction not a sound file so all worlds don’t have to import sound file
Bring electronic copy of homework to class
Bring printed copy of homework to submit