General Computer Science for Engineers CISC 106 James Atlas Computer and Information Sciences 11/16/2009

James Atlas Overview Review Review  Inheritance  Cell Arrays Polymorphism Polymorphism  What is it?  Why use it?  How does it work in Matlab?

James Atlas Inheritance The is a relationship The is a relationship Inheritance Hierarchy Inheritance Hierarchy  state (properties)  behavior (methods) Superclass Superclass Subclass Subclass Animal ReptileBird

James Atlas Cell Arrays Normal array Normal array zeros(1,5) is 5 doubles [ ] is 4 doubles Cell array Cell array { } is 4 cells, each with a 1x1 array of double values inside

James Atlas What is a cell? A cell is like a window into a room, and inside the room can be data of any size A cell is like a window into a room, and inside the room can be data of any size A cell array is like a hallway with many doors A cell array is like a hallway with many doors Student age=19 name=‘Joe’ credits=78 ‘hello’ normal arraycell array

James Atlas Polymorphism: What is It?

James Atlas Polymorphism: What is It? One name, many forms One name, many forms  Capability to perform different actions based on the object instance

James Atlas Polymorphism: What is It? One name, many forms One name, many forms  Capability to perform different actions based on the object instance Each band member is a Musician Each band member is a Musician  We could tell all band members to Play  Play for a drummer would perform a different action than Play for a guitarist

James Atlas Polymorphism: Why use it? Easily extensible systems Easily extensible systems  Add new features with low impact on system

James Atlas Polymorphism: Why use it? Easily extensible systems Easily extensible systems  Add new features with low impact on system For example, we are hosting American Idol for Musicians For example, we are hosting American Idol for Musicians  In Season 1 we have guitarists, drummers, and pianists  In Season 2 we add keyboardists, trumpeters and bagpipers

James Atlas Polymorphism: Why use it? Easily extensible systems Easily extensible systems  Add new features with low impact on system For example, we are hosting American Idol for Musicians For example, we are hosting American Idol for Musicians  In Season 1 we have guitarists, drummers, and pianists  In Season 2 we add keyboardists, trumpeters and bagpipers  We don’t need to change the competition format or hosting protocol!

James Atlas Polymorphism: How does it work in Matlab? Overriding Overriding Matlab constructs Matlab constructs  Methods (the behavior)  Classes  Abstract tag

James Atlas Shape.m Class classdef Shape properties properties center_x center_x center_y center_y color color end end methods (Abstract) methods (Abstract) result = area(shape) result = area(shape) handle = draw(shape) handle = draw(shape) end endend

James Atlas Circle.m Class classdef Circle < Shape properties properties radius radius end end methods methods function circle = Circle(center_x, center_y, radius, color) function circle = Circle(center_x, center_y, radius, color) circle.center_x = center_x; circle.center_x = center_x; circle.center_y = center_y; circle.center_y = center_y; circle.radius = radius; circle.radius = radius; circle.color = color; circle.color = color; end end...endend

James Atlas Circle.m Class (cont’) classdef Circle < Shape methods methods... function handle = draw(circle) function handle = draw(circle) handle = rectangle('Position', [... handle = rectangle('Position', [... circle.center_x - circle.radius,... circle.center_x - circle.radius,... circle.center_y - circle.radius,... circle.center_y - circle.radius,... 2 * circle.radius,... 2 * circle.radius,... 2 * circle.radius],... 2 * circle.radius],... 'Curvature', [1 1], 'FaceColor', circle.color); 'Curvature', [1 1], 'FaceColor', circle.color); end end...endend

James Atlas Circle.m Class (cont’) classdef Circle < Shape methods methods... function result = area(circle) function result = area(circle) result = pi * circle.radius * circle.radius; result = pi * circle.radius * circle.radius; end endendend

James Atlas Example: Shape sorter Create rectangle and triangle Create rectangle and triangle Create a cell array of shapes Create a cell array of shapes Update each shape’s x and y center Update each shape’s x and y center Draw shapes and then put them in order by area Draw shapes and then put them in order by area Animate swaps Animate swaps