Object Oriented Programing Writing computer programs Based on
Objects Instead of Actions Based on Data Instead of Logic
Slide 3
Traditional Programming Input Data Process the Data using Logic
Output the Data Example: Add 2 Numbers Input Data Get Number 1 Get
Number 2 Process the Data Add Number 1 + Number 2 Output the Data
The Answer is: _______
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Object Oriented Programming Focus is on the Object we want to
Manipulate/Change Person Animal (Scratch the Cat) Building Buttons
/ Icons Identify What Objects You Need How do the Objects Relate to
Each Other
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Objects All Objects have 3 Parts Properties What the Object
looks like Methods Things the Objects can do Events What activities
(by the user or by the computer) that the object responds to
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Our Programming Example Dog vs. Cat The cat and dog will walk
up to one another and say hi (bark and meow) Object Oriented
Programming What objects will we need? (Objects and Properties)
What do the objects need to do? (Methods) When do they need to do
these things? (Events)
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Lets Get Programming Start Scratch the Cat Double Click on the
Scratch Icon
Slide 8
Scratch Interface Methods and Events Code Objects Display
Properties
Slide 9
Objects What Objects do You Need? Cat Dog Cat Already Exists
(Scratch) Set Properties for Scratch
Edit Properties Change the Size Make Smaller ?????
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Add Sound Properties Sounds
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Add Sound Scratch already has One Sound MEOW Add Another Sound
Import Animal Cat OK 1) Import 2) Animal 3) Cat
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Add A 2 nd Object - DOG Add New Sprite (Object) Add New
Sprite
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Add a 2 nd Object - Dog Look Familiar What Should We Do??
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Edit the Object Properties Resize Make Smaller Rotate if Needed
So Dog will Face the Cat
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Add Sound New Objects will not have any existing sounds Add a
Sound Import Animal Dog1 OK 2) Animal 3) Dog1 1) Import
Slide 22
Add Events Events are the Actions Each Object will Respond to
Can be Computer Generated or User Generated Cannot Respond to EVERY
action 1 st Event in this Program Starting the Program When the
User Clicks the Green Flag
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Events Responses to Actions Can be Computer Generated or User
Generated We need to tell the Objects (Cat and Dog) what Actions to
Respond to They cannot respond to everything 1 st Event Starting
the Program When the Green Flag is Clicked 1) Make sure CAT is
Clicked 2) Make sure Scripts is Click Move Objects around using
Mouse to look like this.
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Event When Flag Clicked Flag Event is in the Control Section
Using Mouse Drag to the Script area 1) Control 2) Drag Flag to
Scripts Area
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Methods When Flag Clicked What do we want the Cat to do when
the Flag is Clicked Say Meow Make a Meowing Sound These are Methods
Add Method to Code Window (Attach to Event)
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Method Say Meow Find Method LOOKS section Drag Say HELLO for 2
Secs to Scripts area We dont want Cat to Say Hello Boxes in Methods
are things we can change 1) LOOKS 2) Drag Say Hello to Code
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Method Say Meow Click on Hello box Type MEOW Click on 2 box
Type 1 Test Click the Green Flag (Code a Little Test a LOT)
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Add Next Method Play Sound Add Sound SOUND Section Drag Play
Sound Cat to Scripts Area Change Cat to Meow Test 1) Sound 2) Drag
to Event
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Variables A variable is a placeholder for a number that we dont
know what it is yet, or a number that can change It has a name We
assign it a value when we are ready We can change the value when we
need to Lets include a variable to count how many times the cat
meows
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Make a Variable - Counter Click the VARIABLE section Click on
the Make a Variable option Give the Variable a Name: COUNTER Make
sure For all Sprites is clicked OK 1) Variables 2) Make a Variable
3) Give a Name
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Variable Choices Variable Shows Up
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Give Variable a Value We need to set a Value for our Counter
Variable When all variables are created in Scratch they are given a
value of Zero We need to set it to zero so that it resets everytime
we start over and hit the green flag
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Give Variable a Value Drag Set Counter to 0 method over to the
Scripts Area Put just under Drag to Code List
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Update Value We want to change the value of the counter every
time the cat meows What options do we have to do that??
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Update Value Drag Change Counter by 1 method over to the
Scripts Area Underneath other instructions
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Repeating Actions How many times to we want the cat to meow? 5
times? 10 times? As long as we run the program? We do not want to
have to add more instructions for each time Programmers use
something called a LOOP to repeat Lets have our cat meow 15
times
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Adding a Loop Click on CONTROL section Find the Loop
instructions Drag the instructions to Scripts Area Need to put
above the cat meowing to repeat this action 1) Repeat 2) Put
Here
Slide 38
Adding a Loop Change the 10 value to 15 to loop 15 times Test
It Watch Counter We could use the Forever loop to loop as long as
the program is running Change to 15
Slide 39
Events - Let the Dog Respond The dog has to know that the cat
has meowed Cat has to cause a computer generated event Dog can
respond by barking Broadcast an Event And wait for a response
Slide 40
Create an Event Drag Broadcast to the Scripts Area Click on the
Down Arrow NEW Name the Event CatMeow 1) Drag Broadcast and Wait 2)
Arrow - NEW
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Have Dog Respond Click on the Dog Sprite No Scripts yet for the
Dog Object
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Have Dog Respond Dog must listen for the CatMeow event Drag
When I receive CatMeow to the Scripts Area When the Cat Meow and
the event fires the Dog will hear it What should the dog do???
Bark
Slide 43
Dog Bark LOOKS Section Drag Say Hello for 2 Secs to Scripts
Area Change Hello to Woof Change 2 secs to 1 sec Test It 1) Drag to
Scripts Area 2) Change to Woof and 1 Sec
Slide 44
Dog Bark SOUND Section Drag Play Sound to Scripts Area Click on
Down Arrow Select Dog1 sound Test It 1) Play Sound 2) Dog1
Sound
Slide 45
Dog Chases Cat Dog moves toward the Cat Move 20 steps Cat moves
away from the Cat Move 10 steps Add Code for Each Object to
Move
Slide 46
Dog Chases Cat Make sure the Dog Object is Selected MOTION
Section Move 10 Steps Change to 20 Steps 1) Dog 2) Move 10 Steps 3)
Change to 20
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Cat Runs from Dog Click Cat Object Motion Move 10 Steps Put
Under Broadcast Test It 1) Pick Cat 2) Move 10 Steps 3) Put into
Scripts
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Clear Method Return the Objects to their Starting Place to Run
Again Clear Method Responds to an Event Move Dog to Location (-125,
-30) Move Cat to Starting Location (135, -15) Uses Pixel numbers
(0,0) is the middle of the screen
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Clear Method 1) Cat 3) When I Receive Event 2) CONTROL
Slide 50
Create the Event Drag to the Scripts Area NOT part of other
instructions Click on the CatMeow Box Click NEW to create a new
Event Name Event CLEAR
Slide 51
Move the Cat Locations use an X and Y values for Height and
Width MOTION Section Set X to 0 Set Y to 0 Change X to 135 Change Y
to -15 1) Set X to 0 2) Set Y to 0 3) Change Values
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Broadcast the Clear Event Make the Clear Event Happen Beginning
of Program 1) CONTROL 2) Broadcast CatMeow
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Broadcast the Clear Event CONTROL Section Drag to Top Right
below Click on CatMeow Change to Clear Event 1) Below Flag
Click
Slide 54
Move the Dog Uses the Same Event Still Need to listen for it
(Already being Broadcast) 1) Click Dog Object 3) When I Receive
CatMeow 2) CONTOL
Slide 55
Move the Dog CONTOL Section Drag to the Scripts Area Not part
of other instructions Click on the CatMeow Box Click Clear
event
Slide 56
Move the Dog MOTION Section Set X to 0 Set Y to 0 Change X to
-125 Change Y to -30 1) Set X to 0 2) Set Y to 0 3) Change
Values