MultiKeyComparator.java

/*
 ***************************************************************************************
 *  Copyright (C) 2006 EsperTech, Inc. All rights reserved.                            *
 *  http://www.espertech.com/esper                                                     *
 *  http://www.espertech.com                                                           *
 *  ---------------------------------------------------------------------------------- *
 *  The software in this package is published under the terms of the GPL license       *
 *  a copy of which has been included with this distribution in the license.txt file.  *
 ***************************************************************************************
 */
package com.espertech.esper.util;

import com.espertech.esper.collection.MultiKeyUntyped;

import java.io.Serializable;
import java.text.Collator;
import java.util.Comparator;

/**
 * A comparator on multikeys. The multikeys must contain the same
 * number of values.
 */
public final class MultiKeyComparator implements Comparator<MultiKeyUntyped>, MetaDefItem, Serializable {
    private final boolean[] isDescendingValues;
    private static final long serialVersionUID = -5990983090238885417L;

    /**
     * Ctor.
     *
     * @param isDescendingValues - each value is true if the corresponding (same index)
     *                           entry in the multi-keys is to be sorted in descending order. The multikeys
     *                           to be compared must have the same number of values as this array.
     */
    public MultiKeyComparator(boolean[] isDescendingValues) {
        this.isDescendingValues = isDescendingValues;
    }

    public final int compare(MultiKeyUntyped firstValues, MultiKeyUntyped secondValues) {
        if (firstValues.size() != isDescendingValues.length || secondValues.size() != isDescendingValues.length) {
            throw new IllegalArgumentException("Incompatible size MultiKey sizes for comparison");
        }

        for (int i = 0; i < firstValues.size(); i++) {
            Object valueOne = firstValues.get(i);
            Object valueTwo = secondValues.get(i);
            boolean isDescending = isDescendingValues[i];

            int comparisonResult = compareValues(valueOne, valueTwo, isDescending);
            if (comparisonResult != 0) {
                return comparisonResult;
            }
        }

        // Make the comparator compatible with equals
        if (!firstValues.equals(secondValues)) {
            return -1;
        } else {
            return 0;
        }
    }

    /**
     * Compares two nullable values.
     *
     * @param valueOne     first value to compare
     * @param valueTwo     second value to compare
     * @param isDescending true for descending
     * @return compare result
     */
    protected static int compareValues(Object valueOne, Object valueTwo, boolean isDescending) {
        if (valueOne == null || valueTwo == null) {
            // A null value is considered equal to another null
            // value and smaller than any nonnull value
            if (valueOne == null && valueTwo == null) {
                return 0;
            }
            if (valueOne == null) {
                if (isDescending) {
                    return 1;
                }
                return -1;
            }
            if (isDescending) {
                return -1;
            }
            return 1;
        }

        Comparable comparable1;
        if (valueOne instanceof Comparable) {
            comparable1 = (Comparable) valueOne;
        } else {
            throw new ClassCastException("Cannot sort objects of type " + valueOne.getClass());
        }

        if (isDescending) {
            return -1 * comparable1.compareTo(valueTwo);
        }

        return comparable1.compareTo(valueTwo);
    }

    /**
     * Compares two nullable values using Collator, for use with string-typed values.
     *
     * @param valueOne     first value to compare
     * @param valueTwo     second value to compare
     * @param isDescending true for descending
     * @param collator     the Collator for comparing
     * @return compare result
     */
    public static int compareValuesCollated(Object valueOne, Object valueTwo, boolean isDescending, Collator collator) {
        if (valueOne == null || valueTwo == null) {
            // A null value is considered equal to another null
            // value and smaller than any nonnull value
            if (valueOne == null && valueTwo == null) {
                return 0;
            }
            if (valueOne == null) {
                if (isDescending) {
                    return 1;
                }
                return -1;
            }
            if (isDescending) {
                return -1;
            }
            return 1;
        }

        if (isDescending) {
            return collator.compare(valueTwo, valueOne);
        }

        return collator.compare(valueOne, valueTwo);
    }
}