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Re: 970721: NetCDF Java

> I received mail stating that I should take a look at your progress
> on a Java NetCDF interface. I've taken a quick look (I'll spend some
> more time later) and I have a few preliminary observations/questions.
>
> 1). Will this use/need JDK 1.1?

Yes. Inner classes are used in the implementation, and no attempt
was made to limit use of the java.* classes & interfaces to those
available prior to 1.1

> 2). I was curious about how you've changed the objects from the C++ way
> of doing things. For instance, in C++, the Variable object gets/puts
> data as well as tells you about the variable in question. This is not
> the case in the Java version. I found it very intuitive the C++ way;
> once you got a variable, you could do any operation on it. Why is
> it necessary to still deal with the Netcdf class to actually get/put
> data?

There are a couple of reasons for this.

"Variables which do I/O" don't exist independent of a netcdf file
in the current C++ implementation. It seems to me to be a mistake
to allow construction of an object (Variable in this case) which
has some of it's methods unavailable until/unless it is "bound"
to a netcdf file or other service. The java interface separates
the Variable description (just called "Variable") from
the i/o interface (ArrayInput, ArrayOutput). The container which
provides the I/O service (a netcdf file) is a factory for
these interface objects. In practice, it isn't much different
from what you were doing before. You ask for an object to do I/O
with by name. In terms of it's state information,
the I/O object is more abstract than a netcdf variable, but
you can still inquire the info you are most likely to need at
I/O time: rank, dimension sizes, etc. Variable, ArrayInput, and
ArrayOutput all derive from MultiArray.


> 3). Maybe I didn't look hard enough, but are there classes to create
> NetCDF files?

NetcdfV1File.
The constructors to create a netcdf file are those which
have Variable [], Attribute [] or VariableSet arguments.

> 4). What will the capabilities of the Iterator class(es) be?

Javadoc is not currently generating documentation for inner classes.

For XXX in {Dimension, Attribute, Variable}

public interface XXXSet.Iterator {
        /**
         * Returns <code>true</code> if there are more elements.
         */
        boolean hasNext();

        /**
         * Returns the next element. Calls to this
         * method will step through successive elements.
         * @exception NoSuchElementException If no more elements exist.
         */
        XXX next();
}

The method names are from the proposed java.util.Iterator
class in the Containers proposal. Iterator is to replace or supplant
java.util.Enumeration.

> I guess that's all I have right now. I wanted to thank you for asking
> me to take a look at things. I've been using the Alpha version of
> Jave NetCDF (done by Joe Sirrott I believe). It would be a great help
> to have a version that can write files as well. :)

-glenn