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The main module contains the GeoTools public interfaces that are used by other GeoTools modules (and GeoTools applications). Where possible we make use industry standard terms as provided by OGC and ISO standards. The formal GeoTools public api consists of gt-metadata, jts and the gt-main module. The main module contains the default implementations that are available provided to other GeoTools modules using our factory system. Factories are obtained from an appropriate FactoryFinder, giving applications a chance configure the factory used using the Factory Hints facilities. FilterFactory ff = CommonFactoryFinder.getFilterFactory(); Expression expr = ff.add( expression1, expression2 ); If you find yourself using implementation specific classes chances are you doing it wrong: Expression expr = new AddImpl( expression1, expressiom2 );

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/*
 *    GeoTools - The Open Source Java GIS Toolkit
 *    http://geotools.org
 *
 *    (C) 2004-2008, Open Source Geospatial Foundation (OSGeo)
 *
 *    This library is free software; you can redistribute it and/or
 *    modify it under the terms of the GNU Lesser General Public
 *    License as published by the Free Software Foundation;
 *    version 2.1 of the License.
 *
 *    This library is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *    Lesser General Public License for more details.
 */
package org.geotools.data.store;

import java.util.Iterator;
import java.util.NoSuchElementException;
import org.opengis.feature.simple.SimpleFeature;

/**
 * This iterator is used to indicate that contents could not be aquired.
 *
 * The normal Collection.iterator() method does not let us return an error (we always have to
 * return an iterator). However Iterator.next() can be used to return an NoSuchElementException.
 *
 * So we are basically going to lie, we are going to pretend their is content *once*, and when
 * they ask for it we are going to hit them with a NoSuchElementExcetion. This is a mean trick, but
 * it does convey the idea of asking for content that is supposed to be there and failing to aquire
 * it.
 *
 * @author jgarnett
 * @since 2.1.RC0
 */
public class NoContentIterator implements Iterator {
    Throwable origionalProblem;

    public NoContentIterator(Throwable t) {
        origionalProblem = t;
    }

    public boolean hasNext() {
        return origionalProblem != null;
    }

    public SimpleFeature next() {
        if (origionalProblem == null) {
            // you only get the real error on the first offense
            // (after that you are just silly)
            //
            throw new NoSuchElementException();
        }
        NoSuchElementException cantFind =
                new NoSuchElementException("Could not aquire feature:" + origionalProblem);
        cantFind.initCause(origionalProblem);
        origionalProblem = null;
        throw cantFind;
    }

    public void remove() {
        if (origionalProblem == null) {
            // user did not call next first
            throw new UnsupportedOperationException();
        }
        // User did not call next first
        throw new IllegalStateException();
    }
}