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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;
import org.opengis.style.StyleVisitor;

/**
 * A Displacement gives X and Y offset displacements to use for rendering a text label near a point.
 *
 * @author Ian Turton, CCG
 * @version $Id$
 */
public interface Displacement extends org.opengis.style.Displacement {
    /** Default Displacement instance. */
    static final Displacement DEFAULT =
            new ConstantDisplacement() {
                private void cannotModifyConstant() {
                    throw new UnsupportedOperationException("Constant Stroke may not be modified");
                }

                public Expression getDisplacementX() {
                    return ConstantExpression.ZERO;
                }

                public Expression getDisplacementY() {
                    return ConstantExpression.ZERO;
                }

                public Object accept(StyleVisitor visitor, Object extraData) {
                    cannotModifyConstant();
                    return null;
                }
            };

    /** Null Displacement instance. */
    static final Displacement NULL =
            new ConstantDisplacement() {
                private void cannotModifyConstant() {
                    throw new UnsupportedOperationException("Constant Stroke may not be modified");
                }

                public Expression getDisplacementX() {
                    return ConstantExpression.NULL;
                }

                public Expression getDisplacementY() {
                    return ConstantExpression.NULL;
                }

                public Object accept(StyleVisitor visitor, Object extraData) {
                    cannotModifyConstant();
                    return null;
                }
            };

    /**
     * Returns an expression that computes a pixel offset from the geometry point. This offset point
     * is where the text's anchor point gets located. If this expression is null, the default offset
     * of zero is used.
     *
     * @return Horizontal offeset
     */
    Expression getDisplacementX();

    /** Sets the expression that computes a pixel offset from the geometry point. */
    void setDisplacementX(Expression x);

    /** Sets the expression that computes a pixel offset from the geometry point. */
    void setDisplacementY(Expression y);

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

abstract class ConstantDisplacement implements Displacement {
    private void cannotModifyConstant() {
        throw new UnsupportedOperationException("Constant Displacement may not be modified");
    }

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

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

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

    public void accept(StyleVisitor visitor) {
        cannotModifyConstant();
    }
}