001/*
002 * Copyright (C) 2008 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.collect.testing.testers;
018
019import static com.google.common.collect.testing.features.CollectionFeature.ALLOWS_NULL_VALUES;
020
021import com.google.common.annotations.GwtCompatible;
022import com.google.common.annotations.GwtIncompatible;
023import com.google.common.collect.testing.Helpers;
024import com.google.common.collect.testing.features.CollectionFeature;
025import com.google.common.collect.testing.features.CollectionSize;
026import java.lang.reflect.Method;
027import java.util.Collection;
028
029/**
030 * Tests {@link java.util.Set#hashCode}.
031 *
032 * @author George van den Driessche
033 */
034@GwtCompatible(emulated = true)
035public class SetHashCodeTester<E> extends AbstractSetTester<E> {
036  public void testHashCode() {
037    int expectedHashCode = 0;
038    for (E element : getSampleElements()) {
039      expectedHashCode += ((element == null) ? 0 : element.hashCode());
040    }
041    assertEquals(
042        "A Set's hashCode() should be the sum of those of its elements.",
043        expectedHashCode,
044        getSet().hashCode());
045  }
046
047  @CollectionSize.Require(absent = CollectionSize.ZERO)
048  @CollectionFeature.Require(ALLOWS_NULL_VALUES)
049  public void testHashCode_containingNull() {
050    Collection<E> elements = getSampleElements(getNumElements() - 1);
051    int expectedHashCode = 0;
052    for (E element : elements) {
053      expectedHashCode += ((element == null) ? 0 : element.hashCode());
054    }
055
056    elements.add(null);
057    collection = getSubjectGenerator().create(elements.toArray());
058    assertEquals(
059        "A Set's hashCode() should be the sum of those of its elements (with "
060            + "a null element counting as having a hash of zero).",
061        expectedHashCode,
062        getSet().hashCode());
063  }
064
065  /**
066   * Returns the {@link Method} instances for the test methods in this class which call {@code
067   * hashCode()} on the set values so that set tests on unhashable objects can suppress it with
068   * {@code FeatureSpecificTestSuiteBuilder.suppressing()}.
069   */
070  @GwtIncompatible // reflection
071  public static Method[] getHashCodeMethods() {
072    return new Method[] {
073      Helpers.getMethod(SetHashCodeTester.class, "testHashCode"),
074      Helpers.getMethod(SetHashCodeTester.class, "testHashCode_containingNull")
075    };
076  }
077}