UML 2.0 in a Nutshell

Interfaces

An interface is a classifier that has declarations of properties and methods but no implementations. You can use interfaces to group common elements between classifiers and provide a contract a classifier that provides an implementation of an interface must obey. For example, you can create an interface named Sortable that has one operation named comesBefore(...). Any class that realizes the Sortable interface must provide an implementation of comesBefore(...).

Some modern languages, such as C++, don't support the concept of interfaces; UML interfaces are typically represented as pure abstract classes. Other languages, such as Java, do support interfaces but don't allow them to have properties. The moral is that you should be aware of how your model is going to be implemented when modeling your system.

There are two representations for an interface; which one you should use depends on what you're trying to show. The first representation is the standard UML classifier notation with the stereotype «interface». Figure 2-31 shows the Sortable interface.

Figure 2-31. The Sortable interface

The second representation of an interface is the ball-and-socket notation. This representation shows less detail for the interface but is more convenient for showing relationships to classes. The interface is simply shown as a ball with the name of the interface written below it. Classes ...