Description Matt Whitlock 2007-06-30 06:03:27 EDT

The compiler produces an invalid class file for a top-level class that implements an interface that is parameterized by an inner class of that top-level class when the interface declares a method whose return type is an array of the interface's generic type parameter and the outer class is woven with an aspect.

Attempting to load the invalid class at runtime results in the JVM throwing a ClassFormatError: Duplicate method name&signature in class file.

Example:

////
// pkg1/MyInterface.java
package pkg1;
public interface MyInterface<F> {
	public F[] getValues();
}
////

////
// pkg1/MyClass.java
package pkg1;
public class MyClass implements MyInterface<MyClass.MyInnerEnum> {
	public enum MyInnerEnum {
	}
	public MyInnerEnum[] getValues() {
		return MyInnerEnum.values();
	}
	public static void main(String[] args) {
	}
}
////

////
// pkg2/MyAspect.aj
package pkg2;
import pkg1.MyClass;
public aspect MyAspect pertypewithin(MyClass) {
}
////

Attempting to execute the main method throws this error:

Exception in thread "main" java.lang.ClassFormatError: Duplicate method name&signature in class file pkg1/MyClass
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(Unknown Source)
        at java.security.SecureClassLoader.defineClass(Unknown Source)
        at java.net.URLClassLoader.defineClass(Unknown Source)
        at java.net.URLClassLoader.access$000(Unknown Source)
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClassInternal(Unknown Source)

Deleting the aspect makes the error go away.  Also, changing the declared return type of MyInterface.getValues() to Object[] rather than F[] makes the error go away.