In this paper, we propose a CASE tool platform for Java, called Japid. A CASE tool platform provides various information of source programs and helps CASE tool developers to develop their tools rapidly and easily. Japid has three advanced features: linking fine grained databases dynamically, permitting developers to define their own views, and changing source programs preserving syntactic and semantic constraints. We have made some experiments and developed some CASE tools to show effectiveness of our approach.