/* * Copyright 2002-2012 the original author or authors. * * 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 * * https://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.springframework.util.comparator;import java.util.Comparator;import org.springframework.util.Assert;/** * A Comparator that will safely compare nulls to be lower or higher than * other objects. Can decorate a given Comparator or work on Comparables. * * @author Keith Donald * @author Juergen Hoeller * @since 1.2.2 * @see Comparable */public class NullSafeComparator<T> implements Comparator<T> { /** * A shared default instance of this comparator, treating nulls lower * than non-null objects. */ @SuppressWarnings("rawtypes") public static final NullSafeComparator NULLS_LOW = new NullSafeComparator<Object>(true); /** * A shared default instance of this comparator, treating nulls higher * than non-null objects. */ @SuppressWarnings("rawtypes") public static final NullSafeComparator NULLS_HIGH = new NullSafeComparator<Object>(false); private final Comparator<T> nonNullComparator; private final boolean nullsLow; /** * Create a NullSafeComparator that sorts {@code null} based on * the provided flag, working on Comparables. * <p>When comparing two non-null objects, their Comparable implementation * will be used: this means that non-null elements (that this Comparator * will be applied to) need to implement Comparable. * <p>As a convenience, you can use the default shared instances: * {@code NullSafeComparator.NULLS_LOW} and * {@code NullSafeComparator.NULLS_HIGH}. * @param nullsLow whether to treat nulls lower or higher than non-null objects * @see Comparable * @see #NULLS_LOW * @see #NULLS_HIGH */ @SuppressWarnings({ "unchecked", "rawtypes"}) private NullSafeComparator(boolean nullsLow) { this.nonNullComparator = new ComparableComparator(); this.nullsLow = nullsLow; } /** * Create a NullSafeComparator that sorts {@code null} based on the * provided flag, decorating the given Comparator. * <p>