[CLJ-126] abstract superclass with non-public accessibility

Tue, 24 Aug 2010 04:45:00 -0500

The following code works in Java 6 but not in Java 5:

(def Clojure 1.1.0-alpha-SNAPSHOT
user=> (def s (new StringBuilder "aaa"))
#'user/s
user=> (. s setCharAt (int 0) (char \a))
java.lang.Exception: Unable to resolve symbol: setCharAt in this context

This was discussed on the Clojure mailing list and Stephen C. Gillardi came up with the following conclusion:

_StringBuilder extends AbstractStringBuilder (though the JavaDoc docs lie and say it extends Object). AbstractStringBuilder has default accessibility (not public, protected, or private) which makes the class inaccessible to code outside the java.lang package. In both Java SE 5 and Java SE 6, StringBuilder does not contain a .setCharAt method definition. It relies on the inherited public method in AbstractStringBuilder. (I downloaded the source code for both versions from Sun to check.)

In Java SE 5, when Clojure checks whether or not .setCharAt on StringBuilder is public, it finds that it's a public method of a non-public base class and throws the exception you saw. (It looks like you're using a version of Clojure older than 18 May 2009 (Clojure svn r1371). Versions later than that print the more detailed message I saw.)

In Java SE 6, Clojure's checks for accessibility of this method succeed and the method call works.

I'm not sure whether or not Clojure could be modified to make this method call work in Java 5. Google searches turn up discussion that this pattern of using an undocumented abstract superclass with non-public accessibility is not common in the JDK._

This ticket is being filed in the event that Clojure can handle these types of situations somehow.

Clojure JIRA

[CLJ-126] abstract superclass with non-public accessibility