The imported plug-in contains a Java class that contains the transformation extension rule. Examine the plugin.xml file to understand how to extend the UML-to-Java and Java-to-UML transformations. In the Java class named CustomInterface.java, examine the code in the createTarget method to understand how the transformation extension uses the public API to create a new compilation unit, implement the source interface, and create default methods. In the Java class named FilterImplRule.java, examine the canAccept method to understand how the transformation extension uses Java-to-UML proxy classes to determine which inputs to hide by using filters.