Abstract: A computer implemented method, computer program product, and data processing system for reducing the number of inner classes in a compiled computer program written in an object-oriented programming language. An outer class of the compiled computer program is received, wherein the outer class contains an inner class, wherein the outer class comprises instructions to create an instance of an inner class. The instance is to be used as one of a callback, a listener command, a set of instructions by which an object instance of the inner class transfers information to the corresponding containing instance of the outer class, and combinations thereof. A transformation of the outer class is performed by moving methods of the inner class, as well as their contained instructions, into the outer class. The behavior of the compiled computer program remains unchanged.