1 /* 2 * Copyright (C) 2014 The Dagger Authors. 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package dagger.internal; 18 19 import java.util.ArrayList; 20 import java.util.Collections; 21 import java.util.HashSet; 22 import java.util.LinkedHashMap; 23 import java.util.List; 24 import java.util.Set; 25 26 /** 27 * Collection utility methods in service of Dagger internal classes. <em>Do not use</em> in client 28 * code. 29 */ 30 public final class DaggerCollections { 31 /** 32 * The maximum value for a signed 32-bit integer that is equal to a power of 2. 33 */ 34 private static final int MAX_POWER_OF_TWO = 1 << (Integer.SIZE - 2); 35 DaggerCollections()36 private DaggerCollections() {} 37 38 /** 39 * Returns a new list that is pre-sized to {@code size}, or {@link Collections#emptyList()} if 40 * empty. The list returned is never intended to grow beyond {@code size}, so adding to a list 41 * when the size is 0 is an error. 42 */ presizedList(int size)43 public static <T> List<T> presizedList(int size) { 44 if (size == 0) { 45 return Collections.emptyList(); 46 } 47 return new ArrayList<T>(size); 48 } 49 50 /** 51 * Returns true if at least one pair of items in {@code list} are equals. 52 */ hasDuplicates(List<?> list)53 public static boolean hasDuplicates(List<?> list) { 54 if (list.size() < 2) { 55 return false; 56 } 57 Set<Object> asSet = new HashSet<Object>(list); 58 return list.size() != asSet.size(); 59 } 60 61 /** 62 * Creates a {@link HashSet} instance, with a high enough "intial capcity" that it <em>should</em> 63 * hold {@code expectedSize} elements without growth. 64 */ newHashSetWithExpectedSize(int expectedSize)65 static <T> HashSet<T> newHashSetWithExpectedSize(int expectedSize) { 66 return new HashSet<T>(calculateInitialCapacity(expectedSize)); 67 } 68 69 /** 70 * Creates a {@link LinkedHashMap} instance, with a high enough "initial capacity" that it 71 * <em>should</em> hold {@code expectedSize} elements without growth. 72 */ newLinkedHashMapWithExpectedSize(int expectedSize)73 public static <K, V> LinkedHashMap<K, V> newLinkedHashMapWithExpectedSize(int expectedSize) { 74 return new LinkedHashMap<K, V>(calculateInitialCapacity(expectedSize)); 75 } 76 calculateInitialCapacity(int expectedSize)77 private static int calculateInitialCapacity(int expectedSize) { 78 if (expectedSize < 3) { 79 return expectedSize + 1; 80 } 81 if (expectedSize < MAX_POWER_OF_TWO) { 82 // This is the calculation used in JDK8 to resize when a putAll 83 // happens; it seems to be the most conservative calculation we 84 // can make. 0.75 is the default load factor. 85 return (int) (expectedSize / 0.75F + 1.0F); 86 } 87 return Integer.MAX_VALUE; // any large value 88 } 89 } 90