In this paper, we propose an environment for evolutionary prototyping technique, which is a theoretical framework based on abstract interpretation for Java programs. In general, it is difficult to execute a prototype in the intermediate stage of top-down development. This disadvantage prevents us to find bugs in the early stage of the development. The technique we propose here allows programmers to execute the prototype as a whole, even though it is partially implemented. In the technique, an object is repeatedly changed with interface changes. Our idea is to use an earlier runnable object instead of an unimplemented later object in runtime. The changes of objects are based on abstract interpretation. However, it is necessary to realize the mechanism for using the alternative object including the interface changes in Java. To solve this problem, we introduce proxy object, which is a mediator containing all interface and transform objects dynamically and automatically to keep execution going. Moreover, proxy objects can be automatically generated by the dynamic proxy class API, which is one of Java reflection mechanism. As a result, our environment would reduce the cost that programmers describe code for adjusting current objects.