This paper proposes a system named Addistant, which enables the distributed execution of “legacy” Java bytecode. Here “legacy” means the software originally developed to be executed on a single Java virtual machine (JVM). For adapting legacy software to distributed execution on multiple JVM, developers using Addistant have only to specify the host where instances of each class are allocated and how remote references are implemented. According to that specification, Addistant automatically transforms the bytecode at load time. A technical contribution by Addistant is that it covers a number of issues for implementing distributed execution in the real world. In fact, Addistant can adapt a legacy program written with the Swing library so that Swing objects are executed on a local JVM while the rest of objects are on a remote JVM.