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.testing.testers;
18 
19 import static com.google.common.collect.testing.features.MapFeature.ALLOWS_NULL_KEYS;
20 import static com.google.common.collect.testing.features.MapFeature.ALLOWS_NULL_VALUES;
21 
22 import com.google.common.annotations.GwtCompatible;
23 import com.google.common.collect.testing.AbstractMapTester;
24 import com.google.common.collect.testing.features.CollectionSize;
25 import com.google.common.collect.testing.features.MapFeature;
26 
27 import java.util.Collection;
28 import java.util.Map;
29 
30 /**
31  * Tests {@link java.util.Map#hashCode}.
32  *
33  * @author George van den Driessche
34  * @author Chris Povirk
35  */
36 @GwtCompatible
37 public class MapHashCodeTester<K, V> extends AbstractMapTester<K, V> {
testHashCode()38   public void testHashCode() {
39     int expectedHashCode = 0;
40     for (Map.Entry<K, V> entry : getSampleEntries()) {
41       expectedHashCode += hash(entry);
42     }
43     assertEquals(
44         "A Map's hashCode() should be the sum of those of its entries.",
45         expectedHashCode, getMap().hashCode());
46   }
47 
48   @CollectionSize.Require(absent = CollectionSize.ZERO)
49   @MapFeature.Require(ALLOWS_NULL_KEYS)
testHashCode_containingNullKey()50   public void testHashCode_containingNullKey() {
51     Map.Entry<K, V> entryWithNull = entry(null, samples.e3.getValue());
52     runEntryWithNullTest(entryWithNull);
53   }
54 
55   @CollectionSize.Require(absent = CollectionSize.ZERO)
56   @MapFeature.Require(ALLOWS_NULL_VALUES)
testHashCode_containingNullValue()57   public void testHashCode_containingNullValue() {
58     Map.Entry<K, V> entryWithNull = entry(samples.e3.getKey(), null);
59     runEntryWithNullTest(entryWithNull);
60   }
61 
runEntryWithNullTest(Map.Entry<K, V> entryWithNull)62   private void runEntryWithNullTest(Map.Entry<K, V> entryWithNull) {
63     Collection<Map.Entry<K, V>> entries = getSampleEntries(getNumEntries() - 1);
64 
65     entries.add(entryWithNull);
66 
67     int expectedHashCode = 0;
68     for (Map.Entry<K, V> entry : entries) {
69       expectedHashCode += hash(entry);
70     }
71 
72     resetContainer(getSubjectGenerator().create(entries.toArray()));
73     assertEquals(
74         "A Map's hashCode() should be the sum of those of its entries (where "
75             + "a null element in an entry counts as having a hash of zero).",
76         expectedHashCode, getMap().hashCode());
77   }
78 
hash(Map.Entry<?, ?> e)79   private static int hash(Map.Entry<?, ?> e) {
80     return (e.getKey() == null ? 0 : e.getKey().hashCode())
81         ^ (e.getValue() == null ? 0 : e.getValue().hashCode());
82   }
83 }
84