.UMLCLASS File Extension
What is a UMLCLASS file?
Java class description created using the Unified Modeling Language UML; similar to a .UML file, but used specifically for defining Java classes; may include elements, attributes, and operations associated with the class.
UML class diagrams can be created within the Eclipse IDE by selecting New → Other, then opening the UML 2.x Diagrams directory and choosing "Class Diagram." While UMLCLASS files store data in an XML format, they can be viewed as a visual diagram within Eclipse.