1 /** 2 * Copyright (C) 2014 Google Inc. 3 * Licensed to The Android Open Source Project. 4 * 5 * Licensed under the Apache License, Version 2.0 (the "License"); 6 * you may not use this file except in compliance with the License. 7 * You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 18 package com.android.mail.utils; 19 20 import com.google.android.mail.common.base.Function; 21 import com.google.common.collect.ImmutableMap; 22 23 import java.util.Comparator; 24 import java.util.Map; 25 26 /** 27 * Compares objects of the type {@code T} based on predefined order of the ranks of the type 28 * {@code K}. The ranks that are not in the predefined order will be considered larger than other 29 * ranks (if this comparator is used for sorting those elements will be at the end). 30 * 31 * @param <T> Type to be compared. 32 * @param <K> Type of the ranks used for comparison. 33 */ 34 public class RankedComparator<T, K> implements Comparator<T> { 35 36 private final Map<K, Integer> mRankOrder; 37 38 private final Function<T, K> mRankExtractorFunction; 39 40 /** 41 * Creates a comparator that compares objects of type {@code T} by extracting the ranks of the 42 * objects using {@code rankExtractorFunction} and comparing them by their position in 43 * {@code rankOrder}. Ranks not present in {@code rankOrder} are considered larger than the 44 * ranks present in the {@code rankOrder}. 45 * 46 * @param rankOrder Order of the ranks. 47 * @param rankExtractorFunction Function that extracts rank from the object. 48 */ 49 public RankedComparator(K[] rankOrder, Function<T, K> rankExtractorFunction) { 50 final ImmutableMap.Builder<K, Integer> orderBuilder = ImmutableMap.builder(); 51 for (int i = 0; i < rankOrder.length; i++) { 52 orderBuilder.put(rankOrder[i], i); 53 } 54 mRankOrder = orderBuilder.build(); 55 56 mRankExtractorFunction = rankExtractorFunction; 57 } 58 59 private int getOrder(T object) { 60 final K key = mRankExtractorFunction.apply(object); 61 62 if (mRankOrder.containsKey(key)) { 63 return mRankOrder.get(key); 64 } 65 return Integer.MAX_VALUE; 66 } 67 68 @Override 69 public int compare(T lhs, T rhs) { 70 final int orderLhs = getOrder(lhs); 71 final int orderRhs = getOrder(rhs); 72 // Order can be Integer.MAX_VALUE so subtraction should not be used. 73 return orderLhs < orderRhs ? -1 : (orderLhs == orderRhs ? 0 : 1); 74 } 75 } 76
