Lab Session II
Object-Oriented Specification
Lecturer: Dr. K. Lano
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Figure 1:
Generating Java
Java code can be generated from this model by the option Generate Java in the
‘Synthesis’ menu as shown in Figure 2.
Figure 2:
The code consist of Java classes of each class of Figure 2, in a file Controller.java,
together with the main class, Controller, of the system. A file SystemTypes.java
contains an interface with utility operations (for com- puting OCL expressions), and
ControllerInterface.java contains an interface for Controller. A file GUI.java defines a
simple Swing interface for the system, with buttons for each use case. The file
Controller.java is also displayed to the user (Figure 3).
Figure 3:
Adding an Operation
To add an operation to the class Student click ‘Edit’ on the menu bar and select
‘Modify’. Then click on the “Student” diagram box and select ‘Add Operation’ and
press Ok. First add an integer attribute “year” to Student, then open up the Add
Operation dialog:
Figure 4:
The following window will open.
Figure 5:
Fill the form in the following manner.
Name: progress
Type: none
Parameters: none(leave it blank)
Pre: true
Post: year=year@pre+1
Select Update
The resulting class diagram should be similar to the diagram in the following figure.
Figure 6:
Remember to add ‘year’ as an attribute for class Student (type integer).
Inheritance
Inheritance is one of the characteristic aspects of object-oriented notations, which
distinguishes them from earlier modeling languages such as entity-relationship
diagrams.
Example: every HumanPlayer is also a Player: inheritance represents “is-a” relation
between objects, in contrast to an association, which represents “has-a” relation.
Semantically, set of objects of HumanPlayer is always subset of those of Player.
Figure 7:
Player is called superclass and HumanPlayer subclass in this relationship.
HumanPlayer is said to inherit from Player: each feature (attribute, operation or
association) of Player is also implicitly a feature, with same name and type, of
HumanPlayer, and does not have to be written explicitly on subclass.
*Common mistake: repeating all features of superclass on a subclass.
Continuing with our example. We want to have 2 subclasses (BScStudent and
MScStudent) class that inherent from the “Student” class.
Create classes with the following names: BScStudent and MScStudent. Then select
“Create” from the menu bar and select “Inheritance”. Remember since the “Student”
is the superclass, therefore the target of the inheritance arrow must be pointing at it.
Subclass extends from the Superclass
Generate Java code of your class diagram to see how inheritance looks in the actual
code. The following figure is an example of inheritance in Java.
Figure: 8
Saving your work
In order to save your work, select “File” from the toolbar and click on “Save” option
as shown in the following figure.
Figure 9: