001/* 002 * Copyright 2002-2015 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.util.Assert; 022 023/** 024 * Compares objects based on an arbitrary class order. Allows objects to be sorted based 025 * on the types of class that they inherit, for example: this comparator can be used to 026 * sort a list {@code Number}s such that {@code Long}s occur before {@code Integer}s. 027 * 028 * <p>Only the specified {@code instanceOrder} classes are considered during comparison. 029 * If two objects are both instances of the ordered type this comparator will return a 030 * {@code 0}. Consider combining with a {@link CompoundComparator} if additional sorting 031 * is required. 032 * 033 * @author Phillip Webb 034 * @since 3.2 035 * @see CompoundComparator 036 * @param <T> the type of objects being compared 037 */ 038public class InstanceComparator<T> implements Comparator<T> { 039 040 private final Class<?>[] instanceOrder; 041 042 043 /** 044 * Create a new {@link InstanceComparator} instance. 045 * @param instanceOrder the ordered list of classes that should be used when comparing 046 * objects. Classes earlier in the list will be given a higher priority. 047 */ 048 public InstanceComparator(Class<?>... instanceOrder) { 049 Assert.notNull(instanceOrder, "'instanceOrder' must not be null"); 050 this.instanceOrder = instanceOrder; 051 } 052 053 054 @Override 055 public int compare(T o1, T o2) { 056 int i1 = getOrder(o1); 057 int i2 = getOrder(o2); 058 return (i1 < i2 ? -1 : (i1 == i2 ? 0 : 1)); 059 } 060 061 private int getOrder(T object) { 062 if (object != null) { 063 for (int i = 0; i < this.instanceOrder.length; i++) { 064 if (this.instanceOrder[i].isInstance(object)) { 065 return i; 066 } 067 } 068 } 069 return this.instanceOrder.length; 070 } 071 072}