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 com.google.common.annotations.GwtCompatible;
020import com.google.common.annotations.GwtIncompatible;
021import com.google.common.collect.testing.Helpers;
022import java.lang.reflect.Method;
023
024/**
025 * Tests {@link java.util.List#hashCode}.
026 *
027 * @author George van den Driessche
028 */
029@GwtCompatible(emulated = true)
030public class ListHashCodeTester<E> extends AbstractListTester<E> {
031  public void testHashCode() {
032    int expectedHashCode = 1;
033    for (E element : getOrderedElements()) {
034      expectedHashCode = 31 * expectedHashCode + ((element == null) ? 0 : element.hashCode());
035    }
036    assertEquals(
037        "A List's hashCode() should be computed from those of its elements.",
038        expectedHashCode,
039        getList().hashCode());
040  }
041
042  /**
043   * Returns the {@link Method} instance for {@link #testHashCode()} so that list tests on
044   * unhashable objects can suppress it with {@code FeatureSpecificTestSuiteBuilder.suppressing()}.
045   */
046  @GwtIncompatible // reflection
047  public static Method getHashCodeMethod() {
048    return Helpers.getMethod(ListHashCodeTester.class, "testHashCode");
049  }
050}