Inheritance relation between two classes
Describe an inheritance relation between two classes and show this with a class and subclass in a diagram.
For this discussion consider the UML class diagram below:
For this example, we will talk about shapes specifically 2D and 3D shapes. We do know that the basic elements of a 2D shape have a width and length whereas a 3D shape also has a width and length with an additional dimension called height.
Instead of creating two separate classes for 2D and 3D shape classes that duplicate those elements, it would be better if we use the inheritance relationship. A 3D shape has all the properties of a 2D shape so it makes sense for a 3D shape to inherit the 2D shape properties and include additional properties of its own. Doing so reduces code redundancy.
Overriding Inherited Operations
When the 3D shape extended the 2D shape, we can override some of the inherited operations of the 2D shape. For instance, the 3D shape has to override the “draw()” operation because a 3D shape is drawn differently from a 2D shape. Another example is the “calculate area()” operation which was also overridden in the 3D shape class because the calculation of area is different between 2D and 3D shapes. Additional operations can also be included in the 3D shape such as calculating the volume.
A Link Relation Between Two Classes
Describe a link relation between two classes and show this with a class diagram link. It is not necessary to utilize the same system as for inheritance. For these diagrams, you may keep them simple. All you need to do for each is show two class diagrams and describe the relationship.
For this discussion consider the UML class diagram below:
The scenario is for a typical customer who initiates a transaction with a shop by making orders. So a customer is linked to at least 1 or many orders. The reason why “at least 1” order is because a person doesn’t make him/her a customer not unless he/she bought something from a shop. Moreover, a customer can make multiple orders. On the other hand, each order is linked to only 1 customer.