Jan - Java animation for program understanding

Jan is a system for animated execution of Java programs. Its application area is program understanding rather than debugging. To this end, the animation can be customized, both by annotating the code with visualization directives and by interactively adapting the visual appearance to the user's personal taste. Object diagrams and sequence diagrams are supported. Scalability is achieved by recognizing object composition: object aggregates are displayed in a nested fashion; mechanisms for collapsing and exploding aggregates are provided. Jan has been applied to itself producing an animation of its visualization back-end.