Demeter/Java is an implementation of Adaptive Programming (AP) for Java. Demeter/Java programs consist of Java code together with programs in a small language to express traversals, visitor methods, and class diagrams. Demeter/Java programs are typically written in a preventive maintenance style using traversal strategies for expressing traversals. The resulting programs are very robust under changes to the class diagrams and visitors. This preventive maintenance style also leads to simpler programs, making both software development and maintenance easier.