001/*
002 * Copyright 2002-2019 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
021import org.springframework.lang.Nullable;
022import org.springframework.util.Assert;
023
024/**
025 * Compares objects based on an arbitrary class order. Allows objects to be sorted based
026 * on the types of class that they inherit, for example: this comparator can be used to
027 * sort a list {@code Number}s such that {@code Long}s occur before {@code Integer}s.
028 *
029 * <p>Only the specified {@code instanceOrder} classes are considered during comparison.
030 * If two objects are both instances of the ordered type this comparator will return a
031 * {@code 0}. Consider combining with {@link Comparator#thenComparing(Comparator)}
032 * if additional sorting is required.
033 *
034 * @author Phillip Webb
035 * @since 3.2
036 * @param <T> the type of objects that may be compared by this comparator
037 * @see Comparator#thenComparing(Comparator)
038 */
039public class InstanceComparator<T> implements Comparator<T> {
040
041        private final Class<?>[] instanceOrder;
042
043
044        /**
045         * Create a new {@link InstanceComparator} instance.
046         * @param instanceOrder the ordered list of classes that should be used when comparing
047         * objects. Classes earlier in the list will be given a higher priority.
048         */
049        public InstanceComparator(Class<?>... instanceOrder) {
050                Assert.notNull(instanceOrder, "'instanceOrder' array must not be null");
051                this.instanceOrder = instanceOrder;
052        }
053
054
055        @Override
056        public int compare(T o1, T o2) {
057                int i1 = getOrder(o1);
058                int i2 = getOrder(o2);
059                return (Integer.compare(i1, i2));
060        }
061
062        private int getOrder(@Nullable T object) {
063                if (object != null) {
064                        for (int i = 0; i < this.instanceOrder.length; i++) {
065                                if (this.instanceOrder[i].isInstance(object)) {
066                                        return i;
067                                }
068                        }
069                }
070                return this.instanceOrder.length;
071        }
072
073}