Poor Man’s Genericity for Java is an implementation of parameterized classes (constrained parametric polymorphism) for Java. It is based on a “lowest common denominator” design that can be implemented easily on top of any existing Java compiler. We have implemented a fully working compiler that has been built by reusing Sun’s Java compiler almost without modifications: only the way in which source and byte-code files are loaded was changed to perform simple transformations on loaded files.