Joe-E is a subset of the Java programming language intended to support programming according to object-capability discipline. The language is notable for being an early object-capability subset language. It has influenced later subset languages, such as ADsafe and Caja/Cajita, subsets of Javascript. It is also notable for allowing methods to be verified as functionally pure, based on their method signatures. The restrictions imposed by the Joe-E verifier include: Cup of Joe is slang for coffee, and so serves as a trademark-avoiding reference to Java. Thus, the name Joe-E is intended to suggest an adaptation of ideas from the E programming language to create a variant of the Java language. Waterken Server is written in Joe-E.