Summary

JEP 443: Unnamed Patterns and Variables introduces unnamed variables in Java. The javax.lang.model API need to be updated accordingly.

Problem

JEP 443 repurposes the underscore token (_) to denote unnamed variables in Java in various locations:

• a local variable declaration statement in a block (JLS 14.4.2)
• a resource specification of a try-with-resources statement (JLS 14.20.3)
• the header of a basic for statement (JLS 14.14.1)
• the header of an enhanced for loop (JLS 14.14.2)
• an exception parameter of a catch block (JLS 14.20)
• a formal parameter of a lambda expression (JLS 15.27.1)

When any of the above variable elements is declared with the name _, they denote unnamed variables elements. Moreover, as they do not carry a distinguishable name, they cannot be referred throughout their enclosing scopes.

Solution

We propose the following adjustments to the javax.lang.model API:

• Modify the method javax.lang.model.element.VariableElement::getSimpleName() to return empty name in the case of unnamed variables, making it consistent with unnamed packages, unnamed modules and anonymous classes. The com.sun.source.Tree API also returns an empty name for its version of the name through com.sun.source.tree.VariableTree.getName().
• Add a new predicate method javax.lang.model.element.VariableElement::isUnnamed(). The default implementation of this method examines whether getSimpleName() returns an empty name.

Specification

The proposed API enhancements are attached as specdiff.preliminary.00.zip. These include the changes in javax/lang/model.

The changes to the specification and API are a subject of change until the CSR is finalized.