Components of a Class - MATLAB & Simulink (original) (raw)

Class Building Blocks

MATLAB® organizes class definition code into modular blocks, delimited by keywords. All keywords have an associated end statement:

• classdef...end — Definition of all class components
• properties...end — Declaration of property names, specification of property attributes, assignment of default values
• methods...end — Declaration of method signatures, method attributes, and function code
• events...end — Declaration of event name and attributes
• enumeration...end — Declaration of enumeration members and enumeration values for enumeration classes

properties, methods, events, and enumeration are keywords only within aclassdef block.

Class Definition Block

The classdef block contains the class definition within a file that starts with the classdef keyword and terminates with theend keyword.

classdef (ClassAttributes) ClassName < SuperClass ... end

For example, this classdef defines a class calledMyClass that subclasses the handle class. The class is also defined as sealed, so you cannot use inherit from this class.

classdef (Sealed) MyClass < handle ... end

See classdef for more syntax information.

Properties Block

A properties block contains property definitions, including optional initial values. Use a separate block for each unique set of attribute specifications. Each properties block starts with the properties keyword and terminates with the end keyword.

properties (PropertyAttributes) PropertyName size class {validators} = DefaultValue end

For example, this class defines a private property Prop1 of typedouble with a default value.

classdef MyClass properties (SetAccess = private) Prop1 double = 12 end ... end

See Initialize Property Values for more information.

Methods Block

A methods block contains function definitions for the class methods. Use a separate block for each unique set of attribute specifications. Each methods block starts with the methods keyword and terminates with theend keyword.

methods (MethodAttributes) function obj = MethodName(arg1,...) ... end

For example, this class defines a protected method MyMethod.

classdef MyClass methods (Access = protected) function obj = myMethod(obj,arg1) ... end end end

See Method Syntax for more information.

MATLAB differs from languages like C++ and Java® in that you must explicitly pass an object of the class to the method.

Using the MyClass example, call MyMethod using the object obj of the class and either function or dot syntax:

obj = MyClass; r = MyMethod(obj,arg1); r = obj.MyMethod(arg1);

For more information, see Method Invocation.

Events Block

The events block (one for each unique set of attribute specifications) contains the names of events that this class declares. Theevents block starts with the events keyword and terminates with the end keyword.

classdef ClassName events (EventAttributes) EventName end ... end

For example, this class defined an event called StateChange withListenAccess set to protected.

classdef EventSource events (ListenAccess = protected) StateChanged end ... end

See Events for more information.

Attribute Specification

Attribute Syntax

Attributes modify the behavior of classes and class components (properties, methods, and events). Attributes enable you to define useful behaviors without writing complicated code. For example, you can create a read-only property by setting its SetAccess attribute to private but leaving itsGetAccess attribute set to public.

properties (SetAccess = private) ScreenSize = getScreenSize end

All class definition blocks (classdef,properties, methods, andevents) support specific attributes. All attributes have default values. Specify attribute values only in cases where you want to change from the default value.

Note

Specify the value of a particular attribute only once in any component block.

Attribute Descriptions

For lists of supported attributes, see:

• Class Attributes
• Property Attributes
• Method Attributes
• Event Attributes

Attribute Values

When you specify attribute values, those values affect all the components defined within the defining block. Defining properties with different attribute settings requires multiple properties blocks. Specify multiple attributes in a comma-separated list.

properties (SetObservable = true) AccountBalance end

properties (SetAccess = private, Hidden = true) SSNumber CreditCardNumber end

Simpler Syntax for true/false Attributes

You can use a simpler syntax for attributes whose values aretrue or false. The attribute name alone implies true and adding the not operator (~) to the name implies false. For example, these two ways of defining a static methods block are equivalent.

methods (Static) ... end

methods (Static = true) ... end

Similarly, these three ways of defining a nonstatic methods block are equivalent. All attributes that take a logical value have a default value offalse, so you can omit the attribute to get the default behavior.

methods ... end

methods (~Static) ... end

methods (Static = false) ... end

Enumeration Classes

Enumeration classes are specialized classes that define a fixed set of names representing a single type of value. Enumeration classes use anenumeration block that contains the enumeration members defined by the class.

The enumeration block starts with the enumeration keyword and terminates with the end keyword.

classdef ClassName < SuperClass enumeration EnumerationMember end ... end

For example, this class defines two enumeration members that represent the logical values false and true.

classdef Boolean < logical enumeration No (0) Yes (1) end end

See Define Enumeration Classes for more information.

Related Information

Creating a Simple Class

Folders Containing Class Definitions