Hello Bob
I have already meet the exact same error with other software. It seems
to be caused by a hole in a compatibility later of Java compiler. More
specifically, it is possible to compile a library for Java 8 using a
more recent Java version, for example 17, by specifying the following
option to the Java compiler:
--release 8
Maybe this is what the netCDF project does. When this option is given to
javac, the compiler uses some list of what methods were available in
Java 8, and generate a compiler error if we try to use a Java 17 method
which was not available in Java 8.
Unfortunately there is apparently a grey area not well covered by above
mechanism: covariant return type. The following method existed
(indirectly) in Java 8. I said "indirectly" because it was actually
inherited from the Buffer parent class:
public class ByteBuffer extends Buffer {
public*Buffer* flip();
}
However in Java 9, above method has been overridden has below: the
return type has been specialized from Buffer to ByteBuffer (this is
"return type covariance").
public class ByteBuffer extends Buffer {
public*ByteBuffer* flip();
}
From Java language point of view, methods with the same signature but
covariant return type are the same method. But from the JVM point of
view, if the return type is not exactly the same, this is considered as
two completely different methods. Normally the Java compiler handles
those difference by generating synthetic methods (invisible to Java
developers, except in stack trace when an exception is thrown).
So I believe that this is a hole in the compatibility later of javac,
where it did not recognize that the call to "ByteBuffer flip()" needs to
be replaced by "Buffer flip()". There is two ways to fix this problem:
* Compile with Java 8.
* Or modify the source code with the following change in every place
where a flip() or similar method is invoked on a Buffer subclass:
Replace:
buffer.flip();
By:
((Buffer) buffer).flip();
Martin
