The effectiveness of mutation testing depends heavily on the types of faults that the mutation operators are designed represent. Therefore, the quality of the mutation operators is key to mutation testing. Mutation testing has traditionally been applied to procedural-based languages, and mutation operators have been developed to support most of their language features. Object-oriented programming languages contain new language features, most notably inheritance, polymorphism, and dynamic binding. Not surprisingly, these language features allow new kinds of faults, some of which are not modeled by traditional mutation operators. Although mutation operators for OO languages have previously been suggested, our work in OO faults indicate that the previous operators are insufficient to test these OO language features, particularly at the class testing level. This paper introduces a new set of class mutation operators for the OO language Java. These operators are based on specific OO faults and can be used to detect faults involving inheritance, polymorphism, and dynamic binding, thus are useful for inter-class testing. An initial Java mutation tool has recently been completed, and a more powerful version currently under construction.