Model-based reasoning is a central concept in current research into intelligent diagnostic systems. It is based on the assumption that sources of incorrect behavior in technical devices can be located and identified via the existence of a model describing the basic properties of components of a certain application domain. When actual data concerning the misbehavior of a system composed from such components is available, a domain-independent diagnosis engine can be used to infer which parts of the system contribute to the observed behavior. This paper describes the application of the model-based approach to the debugging of Java programs written in a subset of Java. We show how a simple dependency model can be derived from a program, demonstrate the use of the model for debugging and reducing the required user interactions, give a comparison of the functional dependency model with program slicing, and finally discuss some current research issues.