Using a Class to Display Graphics - MATLAB & Simulink (original) (raw)
Class Calculates Area
The CircleArea class shows the syntax of a typical class definition. This class stores a value for the radius of a circle and calculates the area of the circle when you request this information. CircleArea also implements methods to graph, display, and create objects of the class.
To use the CircleArea class, copy this code into a file named CircleArea.m and save this file in a folder that is on the MATLAB® path.
classdef CircleArea properties Radius end properties (Constant) P = pi end properties (Dependent) Area end methods function obj = CircleArea(r) if nargin > 0 obj.Radius = r; end end function val = get.Area(obj) val = obj.Pobj.Radius^2; end function obj = set.Radius(obj,val) if val < 0 error('Radius must be positive') end obj.Radius = val; end function plot(obj) r = obj.Radius; d = r2; pos = [0 0 d d]; curv = [1 1]; rectangle('Position',pos,'Curvature',curv,... 'FaceColor',[.9 .9 .9]) line([0,r],[r,r]) text(r/2,r+.5,['r = ',num2str(r)]) title(['Area = ',num2str(obj.Area)]) axis equal end function disp(obj) rad = obj.Radius; disp(['Circle with radius: ',num2str(rad)]) end end methods (Static) function obj = createObj prompt = {'Enter the Radius'}; dlgTitle = 'Radius'; rad = inputdlg(prompt,dlgTitle); r = str2double(rad{:}); obj = CircleArea(r); end end end
Use the CircleArea Class
Create an object using the dialog box:
ca = CircleArea.createObj
Add a value for radius and click OK.
Query the area of the defined circle:
Call the overloaded plot method:
Description of Class Definition
| Class definition code begins with the classdef keyword followed by the class name: |
|---|
| classdef CircleArea |
| Define the Radius property within the properties-end keywords. Use default attributes: |
| properties Radius end |
| Define the P property as Constant (Define Class Properties with Constant Values). Call the pi function only once when class is initialized. |
| properties (Constant) P = pi end |
| Define the Area property as Dependent because its value depends on the Radius property. |
| properties (Dependent) Area end |
| The CircleArea class constructor method has the same name as the class and accepts the value of the circle radius as an argument. This method also allows no input arguments. (Class Constructor Methods) |
| methods function obj = CircleArea(r) if nargin > 0 obj.Radius = r; else obj.Radius = 0; end end |
| Because the Area property isDependent, the class does not store its value. Theget.Area method calculates the value of theArea property whenever it is queried. (Get and Set Methods for Dependent Properties) |
| function val = get.Area(obj) val = obj.P*obj.Radius^2; end |
| The set.Radius method tests the value assigned to the Radius property to ensure that the value is not less than zero. MATLAB calls set.Radius to assign a value to Radius. (Property Get and Set Methods) |
| function obj = set.Radius(obj,val) if val < 0 error('Radius must be positive') end obj.Radius = val; end |
| The CircleArea class overloads the plot function. Theplot method uses the rectangle function to create a circle and draws the radius. (Overload Functions in Class Definitions) |
| function plot(obj) r = obj.Radius; d = r*2; pos = [0 0 d d]; curv = [1 1]; rectangle('Position',pos,'Curvature',curv) line([0,r],[r,r]) text(r/2,r+.5,['r = ',num2str(r)]) axis equal end |
| The CircleArea class overloads the disp function to change the way MATLAB displays objects in the command window. |
| function disp(obj) rad = obj.Radius; disp(['Circle with radius: ',num2str(rad)]) end |
| end methods (Static) |
| The CircleArea class defines aStatic method that uses a dialog box to create an object. (Static Methods) |
| function obj = createObj prompt = {'Enter the Radius'}; dlgTitle = 'Radius'; rad = inputdlg(prompt,dlgTitle); r = str2double(rad{:}); obj = CircleArea(r); end |
| End of Static methods block and end of classdef block. |
| end end |