ObjectAid UML Explorer Configuration
After install, you can configure ObjectAid from eclipse, Window->Preferences->Java->ObjectAid->Class Diagram
Generate Class Diagram Using Eclipse Plugin
To create a new Class diagram select File > New > Other and select ObjectAid UML Diagram wizard (See the below screenshot).
select the project source folder and provide file name for the UML Class DIagram (See the below screenshot).
Now you can see test.ucls file inside project src folder. After opening test.ucls file, you can drag and drop the java classes and plugin will automatically generate Class Diagram for you. (See the below screenshot).
After generating the Class Diagram, you can export the same in various formats like png,gif,jpeg etc.