SetHashCodeTester.java revision dbd967a6e5c96cc1a97c5521f88dc1564ba2f81b 
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.collect.testing.features.CollectionFeature;
22import com.google.common.collect.testing.features.CollectionSize;
23
24import java.lang.reflect.Method;
25import java.util.Collection;
26
27/**
28 * Tests {@link java.util.Set#hashCode}.
29 *
30 * <p>This class is GWT compatible.
31 *
32 * @author George van den Driessche
33 */
34public class SetHashCodeTester<E> extends AbstractSetTester<E> {
35  public void testHashCode() {
36    int expectedHashCode = 0;
37    for (E element : getSampleElements()) {
38      expectedHashCode += ((element == null) ? 0 : element.hashCode());
39    }
40    assertEquals(
41        "A Set's hashCode() should be the sum of those of its elements.",
42        expectedHashCode, getSet().hashCode());
43  }
44
45  @CollectionSize.Require(absent = CollectionSize.ZERO)
46  @CollectionFeature.Require(ALLOWS_NULL_VALUES)
47  public void testHashCode_containingNull() {
48    Collection<E> elements = getSampleElements(getNumElements() - 1);
49    int expectedHashCode = 0;
50    for (E element : elements) {
51      expectedHashCode += ((element == null) ? 0 : element.hashCode());
52    }
53
54    elements.add(null);
55    collection = getSubjectGenerator().create(elements.toArray());
56    assertEquals(
57        "A Set's hashCode() should be the sum of those of its elements (with "
58            + "a null element counting as having a hash of zero).",
59        expectedHashCode, getSet().hashCode());
60  }
61
62  /**
63   * Returns the {@link Method} instances for the test methods in this class
64   * which call {@code hashCode()} on the set values so that set tests on
65   * unhashable objects can suppress it with
66   * {@code FeatureSpecificTestSuiteBuilder.suppressing()}.
67   */
68  public static Method[] getHashCodeMethods() {
69    return new Method[]{
70        Platform.getMethod(SetHashCodeTester.class, "testHashCode"),
71        Platform.getMethod(SetHashCodeTester.class, "testHashCode_containingNull") };
72  }
73}
74