The Constructor - New()

A constructor is represented on a class diagram as: Visibility New(ParametersIfAny) and is always the first behavior in the list.

A constructor behavior may require parameters to execute. This solely depends on the requirements of the system and the design of the object. Parameters are required if it makes sense that the object should know something about its state upon creation.

For instance, an object created from the Player class would not make much sense if it's Name state did not have a value. The account status of the object may also be very important to establish. In the diagram below, you will notice that the constructor for the Player object contains a number of parameters.

+New(NewName: String, NewHealth: Integer, AccountStatus: Boolean, NewPassword: String)

As the designer of the class, I have decided that a Player object would not make sense unless all of the states were established at the time of object instantiation, however, the Sword and Flight class do not require any parameters for object instantiation.

Note: A constructor behavior cannot return a value, therefore it is always implemented as a subroutine.

Parameters in Subroutines & Functions

Sometimes a behavior will require further information to accomplish a task. When an input is required for a behavior to execute, this input is passed to the procedure as one or a number of parameters (sometimes called arguments).

Code eg: Subprocedure using parameters.

Public Sub Login(Username As String, Password As String)
    ' Code does something
End Function

Code eg: Function using parameters.

Public Function Calculate(NumberOne As Integer, NumberTwo As Integer) As Integer
    ' Code does something
   Return AValue
End Function