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fastutil extends the Java Collections Framework by providing type-specific maps, sets, lists and priority queues with a small memory footprint and fast access and insertion; provides also big (64-bit) arrays, sets and lists, and fast, practical I/O classes for binary and text files.
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/* Copyright (C) 1991-2016 Free Software Foundation, Inc.
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   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
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   version 2.1 of the License, or (at your option) any later version.

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   You should have received a copy of the GNU Lesser General Public
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   .  */
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/* wchar_t uses Unicode 9.0.0.  Version 9.0 of the Unicode Standard is
   synchronized with ISO/IEC 10646:2014, fourth edition, plus
   Amd. 1  and Amd. 2 and 273 characters from forthcoming  10646, fifth edition.
   (Amd. 2 was published 2016-05-01,
   see https://www.iso.org/obp/ui/#iso:std:iso-iec:10646:ed-4:v1:amd:2:v1:en) */
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/* Assertions (useful to generate conditional code) */
/* Current type and class (and size, if applicable) */
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/*		 
 * Copyright (C) 2003-2016 Paolo Boldi and Sebastiano Vigna
 *
 * 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 it.unimi.dsi.fastutil.chars;

/**
 * A class providing static methods and objects that do useful things with
 * comparators.
 */
public class CharComparators {
	private CharComparators() {
	}

	/** A type-specific comparator mimicking the natural order. */
	protected static class NaturalImplicitComparator extends AbstractCharComparator implements java.io.Serializable {
		private static final long serialVersionUID = 1L;

		public final int compare(final char a, final char b) {
			return (Character.compare((a), (b)));
		}

		private Object readResolve() {
			return NATURAL_COMPARATOR;
		}
	};

	public static final CharComparator NATURAL_COMPARATOR = new NaturalImplicitComparator();

	/**
	 * A type-specific comparator mimicking the opposite of the natural order.
	 */
	protected static class OppositeImplicitComparator extends AbstractCharComparator implements java.io.Serializable {
		private static final long serialVersionUID = 1L;

		public final int compare(final char a, final char b) {
			return -(Character.compare((a), (b)));
		}

		private Object readResolve() {
			return OPPOSITE_COMPARATOR;
		}
	};

	public static final CharComparator OPPOSITE_COMPARATOR = new OppositeImplicitComparator();

	protected static class OppositeComparator extends AbstractCharComparator implements java.io.Serializable {
		private static final long serialVersionUID = 1L;
		private final CharComparator comparator;

		protected OppositeComparator(final CharComparator c) {
			comparator = c;
		}

		public final int compare(final char a, final char b) {
			return comparator.compare(b, a);
		}
	};

	/**
	 * Returns a comparator representing the opposite order of the given
	 * comparator.
	 *
	 * @param c
	 *            a comparator.
	 * @return a comparator representing the opposite order of c.
	 */
	public static CharComparator oppositeComparator(final CharComparator c) {
		return new OppositeComparator(c);
	}
}