PMD provides a very handy method for creating new rules by writing an XPath query. When the XPath query finds a match, a violation is created. Let's take a simple example: assume we have a Factory class that must be always declared final. We'd like to report a violation each time a declaration of Factory is not declared final. Consider the following class:
public class a { Factory f1; void myMethod() { Factory f2; int a; } }The following expression does the magic we need:
//VariableDeclarator [../Type/ReferenceType/ClassOrInterfaceType [@Image = 'Factory'] and ..[@Final='false']]See the XPath rule tutorial for more information.