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      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> {
     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)
     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)
     57   public void testHashCode_containingNullValue() {
     58     Map.Entry<K, V> entryWithNull = entry(samples.e3.getKey(), null);
     59     runEntryWithNullTest(entryWithNull);
     60   }
     61 
     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 
     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