Multi-dispatch in the Java Virtual Machine: Design and implementation

Mainstream object-oriented languages, such as C++ and Java1, provide only a restricted form of polymor-phic methods, namely uni-receiver dispatch. In com-mon programming situations, developers must work around this limitation. We describe how to extend the Java Virtual Machine to support multi-dispatch and ex-amine the complications that Java imposes on multi-dispatch in practice. Our technique avoids changes to the Java programming language itself, maintains source code and library compatibility, and isolates the perfor-mance penalty and semantic changes of multi-method dispatch to the program sections which use it. We have micro-benchmark and application-level performance re-sults for a dynamic Most Specific Applicable (MSA) dispatcher, a framework-based Single Receiver Projec-tions (SRP) dispatcher, and a tuned SRP dispatcher. Our general-purpose technique provides smaller dispatch la-tency than programmer-written double-dispatch code with equivalent functionality.