1 /*
2  * Copyright (C) 2008 The Guava 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 com.google.common.collect;
18 
19 import com.google.common.annotations.GwtCompatible;
20 import java.lang.reflect.Array;
21 import java.util.Arrays;
22 import java.util.Map;
23 import java.util.Set;
24 
25 /**
26  * Methods factored out so that they can be emulated differently in GWT.
27  *
28  * @author Hayward Chan
29  */
30 @GwtCompatible(emulated = true)
31 final class Platform {
32   /** Returns the platform preferred implementation of a map based on a hash table. */
newHashMapWithExpectedSize(int expectedSize)33   static <K, V> Map<K, V> newHashMapWithExpectedSize(int expectedSize) {
34     return CompactHashMap.createWithExpectedSize(expectedSize);
35   }
36 
37   /**
38    * Returns the platform preferred implementation of an insertion ordered map based on a hash
39    * table.
40    */
newLinkedHashMapWithExpectedSize(int expectedSize)41   static <K, V> Map<K, V> newLinkedHashMapWithExpectedSize(int expectedSize) {
42     return CompactLinkedHashMap.createWithExpectedSize(expectedSize);
43   }
44 
45   /** Returns the platform preferred implementation of a set based on a hash table. */
newHashSetWithExpectedSize(int expectedSize)46   static <E> Set<E> newHashSetWithExpectedSize(int expectedSize) {
47     return CompactHashSet.createWithExpectedSize(expectedSize);
48   }
49 
50   /**
51    * Returns the platform preferred implementation of an insertion ordered set based on a hash
52    * table.
53    */
newLinkedHashSetWithExpectedSize(int expectedSize)54   static <E> Set<E> newLinkedHashSetWithExpectedSize(int expectedSize) {
55     return CompactLinkedHashSet.createWithExpectedSize(expectedSize);
56   }
57 
58   /**
59    * Returns the platform preferred map implementation that preserves insertion order when used only
60    * for insertions.
61    */
preservesInsertionOrderOnPutsMap()62   static <K, V> Map<K, V> preservesInsertionOrderOnPutsMap() {
63     return CompactHashMap.create();
64   }
65 
66   /**
67    * Returns the platform preferred set implementation that preserves insertion order when used only
68    * for insertions.
69    */
preservesInsertionOrderOnAddsSet()70   static <E> Set<E> preservesInsertionOrderOnAddsSet() {
71     return CompactHashSet.create();
72   }
73 
74   /**
75    * Returns a new array of the given length with the same type as a reference array.
76    *
77    * @param reference any array of the desired type
78    * @param length the length of the new array
79    */
newArray(T[] reference, int length)80   static <T> T[] newArray(T[] reference, int length) {
81     Class<?> type = reference.getClass().getComponentType();
82 
83     // the cast is safe because
84     // result.getClass() == reference.getClass().getComponentType()
85     @SuppressWarnings("unchecked")
86     T[] result = (T[]) Array.newInstance(type, length);
87     return result;
88   }
89 
90   /** Equivalent to Arrays.copyOfRange(source, from, to, arrayOfType.getClass()). */
copy(Object[] source, int from, int to, T[] arrayOfType)91   static <T> T[] copy(Object[] source, int from, int to, T[] arrayOfType) {
92     return Arrays.copyOfRange(source, from, to, (Class<? extends T[]>) arrayOfType.getClass());
93   }
94 
95   /**
96    * Configures the given map maker to use weak keys, if possible; does nothing otherwise (i.e., in
97    * GWT). This is sometimes acceptable, when only server-side code could generate enough volume
98    * that reclamation becomes important.
99    */
tryWeakKeys(MapMaker mapMaker)100   static MapMaker tryWeakKeys(MapMaker mapMaker) {
101     return mapMaker.weakKeys();
102   }
103 
reduceIterationsIfGwt(int iterations)104   static int reduceIterationsIfGwt(int iterations) {
105     return iterations;
106   }
107 
reduceExponentIfGwt(int exponent)108   static int reduceExponentIfGwt(int exponent) {
109     return exponent;
110   }
111 
checkGwtRpcEnabled()112   static void checkGwtRpcEnabled() {}
113 
Platform()114   private Platform() {}
115 }
116