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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) 2005-2008, 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.feature.visitor;

import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import org.geotools.data.simple.SimpleFeatureCollection;
import org.geotools.factory.CommonFactoryFinder;
import org.geotools.feature.visitor.AverageVisitor.AverageResult;
import org.geotools.feature.visitor.CountVisitor.CountResult;
import org.geotools.filter.IllegalFilterException;
import org.opengis.feature.Feature;
import org.opengis.feature.simple.SimpleFeature;
import org.opengis.feature.simple.SimpleFeatureType;
import org.opengis.feature.type.AttributeDescriptor;
import org.opengis.filter.FilterFactory;
import org.opengis.filter.expression.Expression;

/**
 * Calculates the Sum of an attribute (of a FeatureVisitor)
 *
 * @author Cory Horner, Refractions
 * @since 2.2.M2
 */
public class SumVisitor implements FeatureCalc, FeatureAttributeVisitor {
    private Expression expr;

    SumStrategy strategy;

    public SumVisitor(int attributeTypeIndex, SimpleFeatureType type)
            throws IllegalFilterException {
        FilterFactory factory = CommonFactoryFinder.getFilterFactory(null);
        AttributeDescriptor attributeType = type.getDescriptor(attributeTypeIndex);
        expr = factory.property(attributeType.getLocalName());
        createStrategy(attributeType.getType().getBinding());
    }

    public SumVisitor(String attrName, SimpleFeatureType type) throws IllegalFilterException {
        FilterFactory factory = CommonFactoryFinder.getFilterFactory(null);
        AttributeDescriptor attributeType = type.getDescriptor(attrName);
        expr = factory.property(attributeType.getLocalName());
        createStrategy(attributeType.getType().getBinding());
    }

    public SumVisitor(Expression expr) throws IllegalFilterException {
        this.expr = expr;
    }

    protected void setStrategy(SumStrategy strategy) {
        if (this.strategy == null) {
            this.strategy = strategy;
        }
    }

    public void init(SimpleFeatureCollection collection) {
        // do nothing
    }

    @Override
    public List getExpressions() {
        return Arrays.asList(expr);
    }

    @Override
    public Optional> getResultType(List inputTypes) {
        if (inputTypes == null || inputTypes.size() != 1)
            throw new IllegalArgumentException(
                    "Expecting a single type in input, not " + inputTypes);

        Class type = inputTypes.get(0);
        if (Number.class.isAssignableFrom(type)) {
            return Optional.of(inputTypes);
        }
        throw new IllegalArgumentException(
                "The input type for sum must be numeric, instead this was found: " + type);
    }

    /**
     * Factory method
     *
     * @param type The Class of the attributeType
     * @return The correct strategy class (which returns the correct data type)
     */
    private static SumStrategy createStrategy(Class type) {
        if (type == Integer.class) {
            return new IntegerSumStrategy();
        } else if (type == Long.class) {
            return new LongSumStrategy();
        } else if (type == Float.class) {
            return new FloatSumStrategy();
        } else if (Number.class.isAssignableFrom(type)) {
            return new DoubleSumStrategy();
        }

        return null;
    }

    public void visit(SimpleFeature feature) {
        visit((Feature) feature);
    }

    public void visit(Feature feature) {
        Object value = expr.evaluate(feature);

        if (value != null) {
            if (strategy == null) {
                strategy = createStrategy(value.getClass());
            }

            strategy.add(value);
        }
    }

    public Expression getExpression() {
        return expr;
    }

    public Object getSum() {
        return strategy.getResult();
    }

    public void setValue(Object newSum) {
        strategy = createStrategy(newSum.getClass());
        strategy.add(newSum);
    }

    public void reset() {
        strategy = null;
    }

    public CalcResult getResult() {
        if (strategy == null) {
            return CalcResult.NULL_RESULT;
        }
        return new SumResult(strategy);
    }

    protected interface SumStrategy {
        public void add(Object value);

        public Object getResult();
    }

    static class DoubleSumStrategy implements SumStrategy {
        double number = 0;

        public void add(Object value) {
            number += ((Number) value).doubleValue();
        }

        public Object getResult() {
            return Double.valueOf(number);
        }
    }

    static class FloatSumStrategy implements SumStrategy {
        float number = 0;

        public void add(Object value) {
            number += ((Number) value).floatValue();
        }

        public Object getResult() {
            return Float.valueOf(number);
        }
    }

    static class LongSumStrategy implements SumStrategy {
        long number = 0;

        public void add(Object value) {
            number += ((Number) value).longValue();
        }

        public Object getResult() {
            return Long.valueOf(number);
        }
    }

    static class IntegerSumStrategy implements SumStrategy {
        int number = 0;

        public void add(Object value) {
            number += ((Number) value).intValue();
        }

        public Object getResult() {
            return Integer.valueOf(number);
        }
    }

    public static class SumResult extends AbstractCalcResult {
        private SumStrategy sum;

        public SumResult(SumStrategy newSum) {
            sum = newSum;
        }

        public SumResult(Object value) {
            sum = createStrategy(value.getClass());
            sum.add(value);
        }

        public Object getValue() {
            return sum.getResult();
        }

        public boolean isCompatible(CalcResult targetResults) {
            if (targetResults == CalcResult.NULL_RESULT) return true;
            if (targetResults instanceof SumResult) return true;
            if (targetResults instanceof CountResult) return true;
            return false;
        }

        public CalcResult merge(CalcResult resultsToAdd) {
            if (!isCompatible(resultsToAdd)) {
                throw new IllegalArgumentException("Parameter is not a compatible type");
            }

            if (resultsToAdd == CalcResult.NULL_RESULT) {
                return this;
            }

            if (resultsToAdd instanceof SumResult) {
                // create a new strategy object of the correct dataType
                Number[] sums = new Number[2];
                sums[0] = (Number) sum.getResult();
                sums[1] = (Number) resultsToAdd.getValue();
                SumStrategy newSum = createStrategy(CalcUtil.getObject(sums).getClass());
                // add the two sums
                newSum.add(sums[0]);
                newSum.add(sums[1]);
                return new SumResult(newSum);
            } else if (resultsToAdd instanceof CountResult) {
                // SumResult + CountResult = AverageResult
                int count = resultsToAdd.toInt();
                AverageResult newResult = new AverageResult(count, sum.getResult());

                return newResult;
            } else {
                throw new IllegalArgumentException(
                        "The CalcResults claim to be compatible, but the appropriate merge method has not been implemented.");
            }
        }
    }
}