You can show Java™ association relationships as attributes
in classifiers in Unified Modeling Language (UML) class diagrams.
To show an association as an attribute, in the diagram editor, right-click
an association relationship; then click .
The association is removed from the diagram and is added to the source
classifier as an attribute.
Tip: You can also drag an association onto the attribute
compartment of the source of the association to show the association as an
attribute.