SetHashCodeTester.java revision 3c77433663281544363151bf284b0240dfd22a42 
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
17package com.google.common.collect.testing.testers;
18
19import static com.google.common.collect.testing.features.CollectionFeature.ALLOWS_NULL_VALUES;
20
21import com.google.common.annotations.GwtCompatible;
22import com.google.common.annotations.GwtIncompatible;
23import com.google.common.collect.testing.Helpers;
24import com.google.common.collect.testing.features.CollectionFeature;
25import com.google.common.collect.testing.features.CollectionSize;
26
27import java.lang.reflect.Method;
28import java.util.Collection;
29
30/**
31 * Tests {@link java.util.Set#hashCode}.
32 *
33 * <p>This class is GWT compatible.
34 *
35 * @author George van den Driessche
36 */
37@GwtCompatible(emulated = true)
38public class SetHashCodeTester<E> extends AbstractSetTester<E> {
39  public void testHashCode() {
40    int expectedHashCode = 0;
41    for (E element : getSampleElements()) {
42      expectedHashCode += ((element == null) ? 0 : element.hashCode());
43    }
44    assertEquals(
45        "A Set's hashCode() should be the sum of those of its elements.",
46        expectedHashCode, getSet().hashCode());
47  }
48
49  @CollectionSize.Require(absent = CollectionSize.ZERO)
50  @CollectionFeature.Require(ALLOWS_NULL_VALUES)
51  public void testHashCode_containingNull() {
52    Collection<E> elements = getSampleElements(getNumElements() - 1);
53    int expectedHashCode = 0;
54    for (E element : elements) {
55      expectedHashCode += ((element == null) ? 0 : element.hashCode());
56    }
57
58    elements.add(null);
59    collection = getSubjectGenerator().create(elements.toArray());
60    assertEquals(
61        "A Set's hashCode() should be the sum of those of its elements (with "
62            + "a null element counting as having a hash of zero).",
63        expectedHashCode, getSet().hashCode());
64  }
65
66  /**
67   * Returns the {@link Method} instances for the test methods in this class
68   * which call {@code hashCode()} on the set values so that set tests on
69   * unhashable objects can suppress it with
70   * {@code FeatureSpecificTestSuiteBuilder.suppressing()}.
71   */
72  @GwtIncompatible("reflection")
73  public static Method[] getHashCodeMethods() {
74    return new Method[]{
75        Helpers.getMethod(SetHashCodeTester.class, "testHashCode"),
76        Helpers.getMethod(SetHashCodeTester.class, "testHashCode_containingNull") };
77  }
78}
79