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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) 2003-2008, 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;

import java.io.IOException;
import org.opengis.feature.type.AttributeDescriptor;

/**
 * The low-level attribute reading API. An AttributeReader is responsible for reading a finite set
 * of attributes from an underlying storage format. It provides meta-data regarding the data it can
 * provide, and an iterative, row-based approach for accessing the data.
 *
 * @author Ian Schneider
 * @version $Id$
 * @see AttributeAcceptor
 */
public interface AttributeReader {
    /**
     * The number of attributes this reader can read, i.e the length of a row.
     *
     * @return Number of attribtues this reader can read
     */
    int getAttributeCount();

    /**
     * Retrieve the AttributeType at the given index.
     *
     * @return AttributeType at given index
     */
    AttributeDescriptor getAttributeType(int index) throws ArrayIndexOutOfBoundsException;

    /** Release any resources associated with this reader */
    void close() throws IOException;

    /**
     * Does another set of attributes exist in this reader?
     *
     * @return true if additional content exists for AttributeReader
     */
    boolean hasNext() throws IOException;

    /** Advance the reader to the next set of attributes. */
    void next() throws IOException;

    /**
     * Read the attribute at the given index.
     *
     * @return Object Attribute at given index
     */
    Object read(int index) throws IOException, ArrayIndexOutOfBoundsException;
}