machine { Compiler

Abstract. We exhibit a grey area in the speci cation of Java and of its implementation through the Java Virtual Machine (JVM): the treatment of initialization of classes and interfaces. We report the result of our experiments with di erent implementations of Java, which con rm the theoretical prediction of our work on mathematical models for Java [4] and the JVM [3], namely that the designers of Java and the JVM have used notions of initialization which do not match and which a ict the portability ofJava programs. We show also that concurrent initialization may deadlock and that various current Java compilers violate the initialization semantics through standard optimization techniques