CS320n –Visual Programming

1. CS320n –Visual Programming Class-level Methods and Inheritance – Part 1 Mike Scott (Slides 4-3-1) Thanks to Wanda Dann, Steve Cooper, and Susan Rodger for slides

2. Reminders • Assignment due tonight by 11 pm Class level Methods and Inheritance Part 1

3. What We Will Do Today • Learn about class level methods and inheritance • class work Class level Methods and Inheritance Part 1

4. Animated Actions • Some actions are more naturally associated with a specific class of objects rather than with the overall world. • Examples • A person walking • A wheel rolling • A fish swimming • If the action involves 2 or more objects in the world it should be a world level method Class level Methods and Inheritance Part 1

5. Class-level Methods • Write a method to add abilities / functions / actions / behaviors to a specific class of objects • class-level method • NOT world-level methods • Demo how to build class-level method Class level Methods and Inheritance Part 1

6. An Example • How can we create a skate method for ice skater objects? • We need to: • create a new method for the ice skater • add code to the new method to make it look like the skater “skates” Class level Methods and Inheritance Part 1

7. Demo: The solution • First, to associate the behavior with the ice skater • select the iceSkater tile in the Object Tree • select the methods tab in the details area • click on the "create new method" button Class level Methods and Inheritance Part 1

8. Storyboard for skate • The slide actions • require several motion instructions • … so we’ll break these two actions into smaller pieces • a technique known as stepwise refinement (and abstraction) Skate: Do together move skater forward 2 meters Do in order slide on left leg slide on right leg Class level Methods and Inheritance Part 1

9. An Aside • Shouldn’t the skater already know how to skate? • Should people already know how to walk? • The objects in Alice are simply 3D models created in other programs • articulating, coloring, setting center point • When added to Alice all objects have certain basic behaviors, move, turn, roll, … • programmers must write code for more complex behaviors • CLASS-LEVEL METHODS! Class level Methods and Inheritance Part 1

10. But This Seems So Hard • Anecdote 1: Show Kelly Scott anything “cool” the computer does • Anecdote 2: Finding Nemo. Making the viewer believe Dory can barely say what she is thinking and how sad she is • It is hard. It is complex. Take a look at the penguin method walk Class level Methods and Inheritance Part 1

11. Penguin Method Walk … and there is more after this. Bottom line. Interesting behaviors are usually complex Class level Methods and Inheritance Part 1

12. Refined storyboard for skate Refinement of slideLeft Do in order Lift right leg and turn upper body forward Lower right leg and return body upright Skate: Do together 1) move forward 2 meters 2) Do in order slideLeft slideRight Refinement of slideRight Do in order Lift left leg and turn upper body forward Lower left leg and return body upright Class level Methods and Inheritance Part 1

13. Writing the code • The next step is to translate the design into program code. • For the slideLeft method, a possible translation is: Design step Instruction Lift the right leg turn the right thigh forward Turn upper body forward turn the upper body forward Lower the right leg turn the right thigh backward Return the body upright turn the upper body backward Class level Methods and Inheritance Part 1

14. Demo • Demonstration of • slideLeft • slideRight • skate • Could we parametize slideLeft and slideRight? • should we? Class level Methods and Inheritance Part 1

15. Correspondence of design to code Skate: Do together move skater forward 2 meters Do in order slide on left leg slide on right leg Class level Methods and Inheritance Part 1

16. Question • Writing the methods to make an ice skater perform a skating motion is an intricate task. • Most likely, you would like to reuse these new methods in other worlds. • How can you make the skate method available for an ice skater in a different world? • any other ice skaters in this world DO NOT know how to skate Class level Methods and Inheritance Part 1

17. Answer: Save out as a new class 1) Rename iceSkater as advancedSkater. 2) Save out as a new class. Alice saves the new class as AdcancedSkater.a2c Class level Methods and Inheritance Part 1

18. Inheritance • The AdvancedSkater class • inherits all the properties and methods from the original IceSkater class, and also • has the newly defined methods (skate, slideLeft, slideRight) • In other programming languages, the concept of creating a new class based on a previously defined class is called inheritance. • object oriented programming. As opposed to procedural programming or functional programming o or … Class level Methods and Inheritance Part 1

19. Using CleverSkater • An instance of the CleverSkater class can be added to a new world – use File|Import. Class level Methods and Inheritance Part 1

20. Benefits of Inheritance • Inheritance supports • the reuse of program code -- allows the programmer to write code once and use it again later in different programs. • sharing code with others in a team project • The best code in your program is the code you didn’t have to write! Class level Methods and Inheritance Part 1