Compatible genericity with run-time types for the Java programming language

Abstract

The most serious impediment to writing

Effective and Efficient Compilation of Run-Time Generics in Java

“…Following the standard approach [14,2,19,18], we present details of this translation by examples, showing how a generic source code is translated into a generic source augmented with the code necessary to let objects carry their full run-time type. As a running example we consider the class reported in Figure 1, representing a generic pair of objects.…”

“…This means that any application created with EGO is to be shipped along with this jar, which can then be seen as a system library to be plugged into the JRE, or as a part of the application itself. The reader should notice that this deployment is rather less critical than any other proposed solution to support run-time generics, which require changes in the JVM, in the JRE's class-loader, or translate code using code-specialisation as NextGen [2].…”

“…The long awaited extension of Java with generics is finally shipped with JDK 1.5 (also called J2SE5.0, http://www.java.sun.com) yet without run-time support, thus resulting in a rather incomplete implementation -see e.g. [14,2,19]. Because generic types are simply introduced as a compile-time abstraction to enforce safety, they never enter the run-time domain, hence they hardly integrate with important Java frameworks such as Serialization, Persistence, JavaBeans, and the like -not to mention the limited integration with the standard Java management of types (concerning e.g.…”

“…However, this approach has a well-recognised problem [14,2,18]: generics are never seen as run-time types of objects, therefore any attempt to recover the type of an object always yields the corresponding monomorphic version. For instance, when sending a List<String> object through the net using Java API, the receiver reads an Object element, and can only downcast it to a List -namely, to the raw type list [6].…”

“…On the other hand, pure translation approaches have been proposed which aims to providing generics only through a compiler producing a standard bytecode. Examples are the code-expansion technique of Pizza [13], its optimized version NextGen [2], and the type-passing approach of LM translator [19,18]. Even though these proposals are in principle appealing for their easy deployment, they were initially being considered as "toy" solutions, sometimes addressing in an inadequate way important issues such as performance and backward compatibility.…”