UML Representing an anonymous class in class diagram?

Question

How would one represent a Java anonymous class in a UML class diagram?

Answer 1

Inner (nested) classes are represented in UML with an association adorned with a crossed circle.

Illustration:

Source:

• UML Class Diagrams for Java Programmers, by Robert C. Martin on InformIT.

Answer 2

There are two really anonymous classes in Java First is the non-named inner class. Such as:

class BGThread<T>{...}
...
class TitleEditDlg{
    new BGThread<Props>(cont, true) {
        @Override
        public Props run() {
            ...
        }
    }
 }

A citation from UML standard 2.5 (p.149):

The standard notation for an anonymous InstanceSpecification of an unnamed Classifier is an underlined colon (‘:’).

So, as for anonymous java class, you should create a class block with only : as name and connect the container class to it twice - by container relationship and by one-direction arrow without a dot. From the other side, the : block should connect to the parent class.

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According to the same source, an Anonymous Bound Class, that is the second anonymous class we meet in Java, but often do not notice it, when you use a template/generic class, as in

class BGThread<T>{...}
...
class TitleEditDlg{
   BGThread<String> newThread= new BGThread<String>();
}    

can be shown by two ways:

• As bind dependency, with substitution on it.
• As an intermediate class, with the name of the parent class and substitution in angle brackets. Notice, here the class is anonymous, but the attribute has a name. So, this way you are showing more information.

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