MATLAB Language Object-Oriented Programming Constructors
Example
A constructor is a special method in a class that is called when an instance of an object is created. It is a regular MATLAB function that accepts input parameters but it also must follow certain rules.
Constructors are not required as MATLAB creates a default one. In practice, however, this is a place to define a state of an object. For example, properties can be restricted by specifying attributes. Then, a constructor can initalize such properties by default or user defined values which in fact can sent by input parameters of a constructor.
Calling a constructor of a simple class
This is a simple class Person.
classdef Person
properties
name
surname
address
end
methods
function obj = Person(name,surname,address)
obj.name = name;
obj.surname = surname;
obj.address = address;
end
end
end
The name of a constructor is the same the name of a class. Consequently, constructors are called by the name of its class. A class Person can be created as follows:
>> p = Person('John','Smith','London')
p =
Person with properties:
name: 'John'
surname: 'Smith'
address: 'London'
Calling a constructor of a child class
Classes can be inherited from parent classes if the share common properties or methods. When a class is inherited from another, it is likely that a constructor of a parent class has to be called.
A class Member inherits from a class Person because Member uses the same properties as the class Person but it also adds payment to its definition.
classdef Member < Person
properties
payment
end
methods
function obj = Member(name,surname,address,payment)
obj = obj@Person(name,surname,address);
obj.payment = payment;
end
end
end
Similarly to the class Person, Member is created by calling its constructor:
>> m = Member('Adam','Woodcock','Manchester',20)
m =
Member with properties:
payment: 20
name: 'Adam'
surname: 'Woodcock'
address: 'Manchester'
A constructor of Person requires three input parameters. Member must respect this fact and therefore call a constructor of the class Person with three parameters. It is fulfilled by the line:
obj = obj@Person(name,surname,address);
The example above shows the case when a child class needs information for its parent class. This is why a constructor of Member requires four parameters: three for its parent class and one for itself.
