User controlled object sharing between Java VM instances

String objects, the most commonly used objects in Java programs, are immutable (read-only) and easily identified. Previous analysis of sharing string objects in the Java Virtual Machine showed promising results, however it is clear that sharing a wider set of objects would result in better performance. Automatic object selection for sharing is non-trivial, because in the current state, only read-only objects can be shared. This attribute cannot easily be determined during runtime by an algorithm; the developer on the other hand can. This paper presents the development of an Application Programmer Interface (API) to allow programmers to use the Java Virtual Machine (JVM) internal sharing functionality. Furthermore, we present the usage of the sharing API using open-source software as real-world test cases. The evaluation shows that the balance between memory savings and start-up time overhead is reasonable.