com.google.uzaygezen.core.ListConcatCombiner.java Source code

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Here is the source code for com.google.uzaygezen.core.ListConcatCombiner.java

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/*
 * Copyright (C) 2008 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.uzaygezen.core;

import java.util.List;

import org.apache.commons.lang3.builder.ReflectionToStringBuilder;
import org.apache.commons.lang3.builder.ToStringStyle;

import com.google.common.base.Preconditions;
import com.google.uzaygezen.core.ranges.Range;

/**
 * Filter combiner that works with filters consisting in a list of ranges, and
 * concatenates them. It only works with non-empty lists, and it never produces
 * empty lists. And the input filters must always start and end at the
 * boundaries of the filtered index; all filters produced by this class have
 * that property as well.
 * 
 * @author Daniel Aioanei
 */
public class ListConcatCombiner<T extends Comparable<T>, V extends Content<V>, R extends Range<T, V>>
        implements FilterCombiner<RangeListFilter<T, V, R>, V, R> {

    private final int threshold;

    public ListConcatCombiner(int threshold) {
        Preconditions.checkArgument(threshold > 0, "threshold must be positive");
        this.threshold = threshold;
    }

    public static <T extends Comparable<T>, V extends Content<V>, R extends Range<T, V>> ListConcatCombiner<T, V, R> unbounded() {
        return new ListConcatCombiner<>(Integer.MAX_VALUE);
    }

    /**
     * If the gap is zero, joins the last index range and the first index range
     * into one range that covers both, and keeps the other ranges intact.
     * Otherwise it concatenates the two lists of ranges. Note that we don't use
     * the full information available in {@code gapEstimate}. Instead we extract
     * its signum and use that to optimise the situation when the gap is zero.
     * 
     * @param lower
     *          must not be empty
     * @param higher
     *          must not be empty
     * @return the computed list and whether the threshold was exceeded or one of
     *         the two filters already had potential over-selectivity.
     */
    @Override
    public SelectiveFilter<RangeListFilter<T, V, R>> combine(FilteredIndexRange<RangeListFilter<T, V, R>, R> lower,
            FilteredIndexRange<RangeListFilter<T, V, R>, R> higher, V gapEstimate) {
        checkInputFilteredIndexRange(lower);
        checkInputFilteredIndexRange(higher);
        RangeListFilter<T, V, R> combinedFilter = lower.getFilter().combine(higher.getFilter(), threshold,
                gapEstimate);
        /*
         * Now we'll have the threshold exceeded information in both the filter and
         * as the second element of the pair. The reason is that the caller of this
         * method does not know about RangeListFilter, and instead it only knows
         * that there is a type T representing the filter.
         */
        return SelectiveFilter.of(combinedFilter, combinedFilter.isThresholdExceeded()
                || lower.isPotentialOverSelectivity() || higher.isPotentialOverSelectivity());
    }

    /**
     * Checks some sanity properties of {@code filteredIndexRange}.
     */
    private static <T extends Comparable<T>, V extends Content<V>, R extends Range<T, V>> void checkInputFilteredIndexRange(
            FilteredIndexRange<RangeListFilter<T, V, R>, R> filteredIndexRange) {
        List<R> filter = filteredIndexRange.getFilter().getRangeList();
        Preconditions.checkArgument(filteredIndexRange.getIndexRange().getStart().equals(filter.get(0).getStart()),
                "invalid start");
        Preconditions.checkArgument(
                filteredIndexRange.getIndexRange().getEnd().equals(filter.get(filter.size() - 1).getEnd()),
                "invalid end");
    }

    @Override
    public String toString() {
        return ReflectionToStringBuilder.toString(this, ToStringStyle.SHORT_PREFIX_STYLE);
    }
}