90 lines
2.9 KiB
Java
90 lines
2.9 KiB
Java
/*
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* Copyright (C) 2014 The Dagger Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package dagger.internal;
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import java.util.ArrayList;
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import java.util.Collections;
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import java.util.HashSet;
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import java.util.LinkedHashMap;
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import java.util.List;
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import java.util.Set;
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/**
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* Collection utility methods in service of Dagger internal classes. <em>Do not use</em> in client
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* code.
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*/
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public final class DaggerCollections {
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/**
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* The maximum value for a signed 32-bit integer that is equal to a power of 2.
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*/
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private static final int MAX_POWER_OF_TWO = 1 << (Integer.SIZE - 2);
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private DaggerCollections() {}
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/**
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* Returns a new list that is pre-sized to {@code size}, or {@link Collections#emptyList()} if
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* empty. The list returned is never intended to grow beyond {@code size}, so adding to a list
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* when the size is 0 is an error.
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*/
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public static <T> List<T> presizedList(int size) {
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if (size == 0) {
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return Collections.emptyList();
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}
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return new ArrayList<T>(size);
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}
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/**
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* Returns true if at least one pair of items in {@code list} are equals.
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*/
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public static boolean hasDuplicates(List<?> list) {
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if (list.size() < 2) {
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return false;
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}
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Set<Object> asSet = new HashSet<Object>(list);
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return list.size() != asSet.size();
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}
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/**
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* Creates a {@link HashSet} instance, with a high enough "intial capcity" that it <em>should</em>
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* hold {@code expectedSize} elements without growth.
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*/
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static <T> HashSet<T> newHashSetWithExpectedSize(int expectedSize) {
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return new HashSet<T>(calculateInitialCapacity(expectedSize));
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}
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/**
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* Creates a {@link LinkedHashMap} instance, with a high enough "initial capacity" that it
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* <em>should</em> hold {@code expectedSize} elements without growth.
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*/
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public static <K, V> LinkedHashMap<K, V> newLinkedHashMapWithExpectedSize(int expectedSize) {
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return new LinkedHashMap<K, V>(calculateInitialCapacity(expectedSize));
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}
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private static int calculateInitialCapacity(int expectedSize) {
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if (expectedSize < 3) {
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return expectedSize + 1;
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}
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if (expectedSize < MAX_POWER_OF_TWO) {
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// This is the calculation used in JDK8 to resize when a putAll
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// happens; it seems to be the most conservative calculation we
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// can make. 0.75 is the default load factor.
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return (int) (expectedSize / 0.75F + 1.0F);
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}
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return Integer.MAX_VALUE; // any large value
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}
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}
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