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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) 2002-2008, 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.styling;

import org.geotools.filter.ConstantExpression;
import org.opengis.filter.expression.Expression;

/**
 * An AnchorPoint identifies the location inside a label or graphic to use as an "anchor" for
 * positioning it relative to a point geometry.
 *
 * @author Ian Turton
 * @version $Id$
 */
public interface AnchorPoint extends org.opengis.style.AnchorPoint {
    // TODO: add AnchorPoint to GeoAPI
    /**
     * get the x coordinate of the anchor point
     *
     * @return the expression which represents the X coordinate
     */
    Expression getAnchorPointX();

    static final AnchorPoint DEFAULT =
            new AnchorPoint() {
                private void cannotModifyConstant() {
                    throw new UnsupportedOperationException("Constant Stroke may not be modified");
                }

                public void setAnchorPointX(Expression x) {
                    cannotModifyConstant();
                }

                public void setAnchorPointY(Expression y) {
                    cannotModifyConstant();
                }

                public void accept(org.geotools.styling.StyleVisitor visitor) {
                    cannotModifyConstant();
                }

                public Object accept(org.opengis.style.StyleVisitor visitor, Object data) {
                    cannotModifyConstant();
                    return null;
                }

                public Expression getAnchorPointX() {
                    return ConstantExpression.constant(0.5);
                }

                public Expression getAnchorPointY() {
                    return ConstantExpression.constant(0.5);
                }
            };

    /**
     * Set the X coordinate for the anchor point
     *
     * @param x an expression which represents the X coordinate
     */
    void setAnchorPointX(Expression x);

    /**
     * set the Y coordinate for the anchor point
     *
     * @param y an expression which represents the Y coordinate
     */
    void setAnchorPointY(Expression y);

    /**
     * calls the visit method of a StyleVisitor
     *
     * @param visitor the style visitor
     */
    void accept(org.geotools.styling.StyleVisitor visitor);
}