We present the design and implementation of dart2java, an experimental Dart to Java compiler. It is implemented in Dart and currently supports many but not all Dart language constructs. dart2java is a playground to evaluate performance implications of running Dart code on the JVM and to investigate if it is possible to write Dart code in a largely Java-dominated environment. This paper describes the architecture of dart2java, performance optimizations such as non-nullability of primitive types and generic specialization (and their implications), as well as ideas for language interoperability, i.e., calling Java code from Dart and vice versa.