org.apache.lucene.util.CollectionUtil.java Source code

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Here is the source code for org.apache.lucene.util.CollectionUtil.java

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.lucene.util;

import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.RandomAccess;

/**
 * Methods for manipulating (sorting) collections.
 * Sort methods work directly on the supplied lists and don't copy to/from arrays
 * before/after. For medium size collections as used in the Lucene indexer that is
 * much more efficient.
 *
 * @lucene.internal
 */

public final class CollectionUtil {

    private CollectionUtil() {
    } // no instance

    private static final class ListIntroSorter<T> extends IntroSorter {

        T pivot;
        final List<T> list;
        final Comparator<? super T> comp;

        ListIntroSorter(List<T> list, Comparator<? super T> comp) {
            super();
            if (!(list instanceof RandomAccess))
                throw new IllegalArgumentException("CollectionUtil can only sort random access lists in-place.");
            this.list = list;
            this.comp = comp;
        }

        @Override
        protected void setPivot(int i) {
            pivot = list.get(i);
        }

        @Override
        protected void swap(int i, int j) {
            Collections.swap(list, i, j);
        }

        @Override
        protected int compare(int i, int j) {
            return comp.compare(list.get(i), list.get(j));
        }

        @Override
        protected int comparePivot(int j) {
            return comp.compare(pivot, list.get(j));
        }

    }

    private static final class ListTimSorter<T> extends TimSorter {

        final List<T> list;
        final Comparator<? super T> comp;
        final T[] tmp;

        @SuppressWarnings("unchecked")
        ListTimSorter(List<T> list, Comparator<? super T> comp, int maxTempSlots) {
            super(maxTempSlots);
            if (!(list instanceof RandomAccess))
                throw new IllegalArgumentException("CollectionUtil can only sort random access lists in-place.");
            this.list = list;
            this.comp = comp;
            if (maxTempSlots > 0) {
                this.tmp = (T[]) new Object[maxTempSlots];
            } else {
                this.tmp = null;
            }
        }

        @Override
        protected void swap(int i, int j) {
            Collections.swap(list, i, j);
        }

        @Override
        protected void copy(int src, int dest) {
            list.set(dest, list.get(src));
        }

        @Override
        protected void save(int i, int len) {
            for (int j = 0; j < len; ++j) {
                tmp[j] = list.get(i + j);
            }
        }

        @Override
        protected void restore(int i, int j) {
            list.set(j, tmp[i]);
        }

        @Override
        protected int compare(int i, int j) {
            return comp.compare(list.get(i), list.get(j));
        }

        @Override
        protected int compareSaved(int i, int j) {
            return comp.compare(tmp[i], list.get(j));
        }

    }

    /**
     * Sorts the given random access {@link List} using the {@link Comparator}.
     * The list must implement {@link RandomAccess}. This method uses the intro sort
     * algorithm, but falls back to insertion sort for small lists.
     * @throws IllegalArgumentException if list is e.g. a linked list without random access.
     */
    public static <T> void introSort(List<T> list, Comparator<? super T> comp) {
        final int size = list.size();
        if (size <= 1)
            return;
        new ListIntroSorter<>(list, comp).sort(0, size);
    }

    /**
     * Sorts the given random access {@link List} in natural order.
     * The list must implement {@link RandomAccess}. This method uses the intro sort
     * algorithm, but falls back to insertion sort for small lists.
     * @throws IllegalArgumentException if list is e.g. a linked list without random access.
     */
    public static <T extends Comparable<? super T>> void introSort(List<T> list) {
        final int size = list.size();
        if (size <= 1)
            return;
        introSort(list, Comparator.naturalOrder());
    }

    // Tim sorts:

    /**
     * Sorts the given random access {@link List} using the {@link Comparator}.
     * The list must implement {@link RandomAccess}. This method uses the Tim sort
     * algorithm, but falls back to binary sort for small lists.
     * @throws IllegalArgumentException if list is e.g. a linked list without random access.
     */
    public static <T> void timSort(List<T> list, Comparator<? super T> comp) {
        final int size = list.size();
        if (size <= 1)
            return;
        new ListTimSorter<>(list, comp, list.size() / 64).sort(0, size);
    }

    /**
     * Sorts the given random access {@link List} in natural order.
     * The list must implement {@link RandomAccess}. This method uses the Tim sort
     * algorithm, but falls back to binary sort for small lists.
     * @throws IllegalArgumentException if list is e.g. a linked list without random access.
     */
    public static <T extends Comparable<? super T>> void timSort(List<T> list) {
        final int size = list.size();
        if (size <= 1)
            return;
        timSort(list, Comparator.naturalOrder());
    }

}