001/*
002 * Copyright 2002-2018 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.util.comparator;
018
019import java.util.Comparator;
020
021/**
022 * Convenient entry point with generically typed factory methods
023 * for common Spring {@link Comparator} variants.
024 *
025 * @author Juergen Hoeller
026 * @since 5.0
027 */
028public abstract class Comparators {
029
030        /**
031         * Return a {@link Comparable} adapter.
032         * @see ComparableComparator#INSTANCE
033         */
034        @SuppressWarnings("unchecked")
035        public static <T> Comparator<T> comparable() {
036                return ComparableComparator.INSTANCE;
037        }
038
039        /**
040         * Return a {@link Comparable} adapter which accepts
041         * null values and sorts them lower than non-null values.
042         * @see NullSafeComparator#NULLS_LOW
043         */
044        @SuppressWarnings("unchecked")
045        public static <T> Comparator<T> nullsLow() {
046                return NullSafeComparator.NULLS_LOW;
047        }
048
049        /**
050         * Return a decorator for the given comparator which accepts
051         * null values and sorts them lower than non-null values.
052         * @see NullSafeComparator#NullSafeComparator(boolean)
053         */
054        public static <T> Comparator<T> nullsLow(Comparator<T> comparator) {
055                return new NullSafeComparator<>(comparator, true);
056        }
057
058        /**
059         * Return a {@link Comparable} adapter which accepts
060         * null values and sorts them higher than non-null values.
061         * @see NullSafeComparator#NULLS_HIGH
062         */
063        @SuppressWarnings("unchecked")
064        public static <T> Comparator<T> nullsHigh() {
065                return NullSafeComparator.NULLS_HIGH;
066        }
067
068        /**
069         * Return a decorator for the given comparator which accepts
070         * null values and sorts them higher than non-null values.
071         * @see NullSafeComparator#NullSafeComparator(boolean)
072         */
073        public static <T> Comparator<T> nullsHigh(Comparator<T> comparator) {
074                return new NullSafeComparator<>(comparator, false);
075        }
076
077}