Classes / Objects / Methods Chapter 4

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

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.

Class Properties Characteristics Methods Behaviors

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

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)

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

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

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

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

Add Method Instructions

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.

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

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

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

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

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

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

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

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

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?

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

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

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.

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

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

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

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

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

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