Subclass built-in numeric types to create customized data types that inherit the functionality of the built-in type. Add functionality to that provided by the superclass by implementing class methods. Subclasses without properties store numeric data as the superclass type. If your subclass design does not require properties to store other data, the implementation is simpler because you do not need to define indexing and concatenation methods.
For more information, see Subclasses of MATLAB Built-In Types.
This example shows a class derived from the built-in
uint8 class. This class simplifies the process of maintaining a collection of intensity image data defined by
uint8 values. The basic operations of the class include:
Capability to convert various classes of image data to
uint8 to reduce object data storage.
A method to display the intensity images contained in the subclass objects.
Ability to use all the methods supported by
uint8 data (for example,
fft, arithmetic operators, and so on).
The class data are matrices of intensity image data stored in the superclass part of the subclass object. This approach requires no properties.
DocUint8 class stores the image data, which converts the data, if necessary:
classdef DocUint8 < uint8 methods function obj = DocUint8(data) if nargin == 0 data = uint8(0); end obj = obj@uint8(data); % Store data on superclass end function h = showImage(obj) data = uint8(obj); figure; colormap(gray(256)) h = imagesc(data,[0 255]); axis image brighten(.2) end end end
DocUint8 class provides a method to display all images stored as
DocUint8 objects in a consistent way. For example:
cir = imread('circuit.tif'); img1 = DocUint8(cir); img1.showImage;
uint8, you can use any
uint8 methods. For example,
ans = 280 272
returns the size of the image data.
Inherited methods perform indexing operations, but return objects of the same class as the subclass.
Therefore, you can index into the image data and call a subclass method:
Subscripted reference operations (controlled by the inherited
subsref method) return a
You can assign values to indexed elements:
img1(100:120,140:160) = 255; img1.showImage;
Subscripted assignment operations (controlled by the inherited
subsasgn method) return a
Concatenation operations work on
DocUint8 objects because this class inherits the
vertcat methods, which return a
Methods that operate on data values, such as arithmetic operators, always return an object of the built-in type (not of the subclass type). For example, multiplying
DocUint8 objects returns a
uint8 object, so calling
showImage throws an error:
a = img1.*1.8; showImage(a);
Check for missing argument or incorrect argument data type in call to function 'showImage'.
To perform operations of this type, implement a subclass method to override the inherited method. The
times method implements array (element-by-element) multiplication.
Add this method to the
function o = times(obj,val) u8 = uint8(obj).*val; o = DocUint8(u8); end
When you override a
uint8 method, MATLAB® calls the subclass method, not the base class method. The subclass method must:
times method on the
DocUint8 object data.
Construct a new
DocUint8 object using the
After adding the
times method to the
DocUint8 class, the output of multiplication expressions is an object of the