package org.apache.lucene.util;
/*
* 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.
*/
import java.util.Comparator;
import java.util.Collections;
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
/** SorterTemplate with custom {@link Comparator} */
private static <T> SorterTemplate getSorter(final List<T> list, final Comparator<? super T> comp) {
if (!(list instanceof RandomAccess))
throw new IllegalArgumentException("CollectionUtil can only sort random access lists in-place.");
return new SorterTemplate() {
@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 void setPivot(int i) {
pivot = list.get(i);
}
@Override
protected int comparePivot(int j) {
return comp.compare(pivot, list.get(j));
}
private T pivot;
};
}
/** Natural SorterTemplate */
private static <T extends Comparable<? super T>> SorterTemplate getSorter(final List<T> list) {
if (!(list instanceof RandomAccess))
throw new IllegalArgumentException("CollectionUtil can only sort random access lists in-place.");
return new SorterTemplate() {
@Override
protected void swap(int i, int j) {
Collections.swap(list, i, j);
}
@Override
protected int compare(int i, int j) {
return list.get(i).compareTo(list.get(j));
}
@Override
protected void setPivot(int i) {
pivot = list.get(i);
}
@Override
protected int comparePivot(int j) {
return pivot.compareTo(list.get(j));
}
private T pivot;
};
}
/**
* Sorts the given random access {@link List} using the {@link Comparator}.
* The list must implement {@link RandomAccess}. This method uses the quick 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 quickSort(List<T> list, Comparator<? super T> comp) {
final int size = list.size();
if (size <= 1) return;
getSorter(list, comp).quickSort(0, size-1);
}
/**
* Sorts the given random access {@link List} in natural order.
* The list must implement {@link RandomAccess}. This method uses the quick 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 quickSort(List<T> list) {
final int size = list.size();
if (size <= 1) return;
getSorter(list).quickSort(0, size-1);
}
// mergeSorts:
/**
* Sorts the given random access {@link List} using the {@link Comparator}.
* The list must implement {@link RandomAccess}. This method uses the merge 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 mergeSort(List<T> list, Comparator<? super T> comp) {
final int size = list.size();
if (size <= 1) return;
getSorter(list, comp).mergeSort(0, size-1);
}
/**
* Sorts the given random access {@link List} in natural order.
* The list must implement {@link RandomAccess}. This method uses the merge 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 mergeSort(List<T> list) {
final int size = list.size();
if (size <= 1) return;
getSorter(list).mergeSort(0, size-1);
}
// insertionSorts:
/**
* Sorts the given random access {@link List} using the {@link Comparator}.
* The list must implement {@link RandomAccess}. This method uses the insertion sort
* algorithm. It is only recommended to use this algorithm for partially sorted small lists!
* @throws IllegalArgumentException if list is e.g. a linked list without random access.
*/
public static <T> void insertionSort(List<T> list, Comparator<? super T> comp) {
final int size = list.size();
if (size <= 1) return;
getSorter(list, comp).insertionSort(0, size-1);
}
/**
* Sorts the given random access {@link List} in natural order.
* The list must implement {@link RandomAccess}. This method uses the insertion sort
* algorithm. It is only recommended to use this algorithm for partially sorted small lists!
* @throws IllegalArgumentException if list is e.g. a linked list without random access.
*/
public static <T extends Comparable<? super T>> void insertionSort(List<T> list) {
final int size = list.size();
if (size <= 1) return;
getSorter(list).insertionSort(0, size-1);
}
}