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.Helpers.getMethod;
020
021import com.google.common.annotations.GwtCompatible;
022import com.google.common.annotations.GwtIncompatible;
023import com.google.common.annotations.J2ktIncompatible;
024import java.lang.reflect.Method;
025
026/**
027 * Tests {@link java.util.List#hashCode}.
028 *
029 * @author George van den Driessche
030 */
031@GwtCompatible
032public class ListHashCodeTester<E> extends AbstractListTester<E> {
033  public void testHashCode() {
034    int expectedHashCode = 1;
035    for (E element : getOrderedElements()) {
036      expectedHashCode = 31 * expectedHashCode + ((element == null) ? 0 : element.hashCode());
037    }
038    assertEquals(
039        "A List's hashCode() should be computed from those of its elements.",
040        expectedHashCode,
041        getList().hashCode());
042  }
043
044  /**
045   * Returns the {@link Method} instance for {@link #testHashCode()} so that list tests on
046   * unhashable objects can suppress it with {@code FeatureSpecificTestSuiteBuilder.suppressing()}.
047   */
048  @J2ktIncompatible
049  @GwtIncompatible // reflection
050  public static Method getHashCodeMethod() {
051    return getMethod(ListHashCodeTester.class, "testHashCode");
052  }
053}