Applying Optimizations for Dynamically-typed Languages to Java

While Java is a statically-typed language, some of its features make it behave like a dynamically-typed language at run time. This includes Java's boxing of primitive values as well as generics, which rely on type erasure. This paper investigates how runtime technology for dynamically-typed languages such as JavaScript and Python can be used for Java bytecode. Using optimistic optimizations, we specialize bytecode instructions that access references in such a way, that they can handle primitive data directly and also specialize data structures in order to avoid boxing for primitive types. Our evaluation shows that these optimizations can be successfully applied to a statically-typed language such as Java and can also improve performance significantly. With this approach, we get an efficient implementation of Java's generics, avoid changes to the Java language, and maintain backwards compatibility, allowing existing code to benefit from our optimization transparently.