ListHashCodeTester.java revision 0888a09821a98ac0680fad765217302858e70fa4 
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 com.google.common.annotations.GwtCompatible;
20import com.google.common.annotations.GwtIncompatible;
21import com.google.common.collect.testing.Helpers;
22
23import java.lang.reflect.Method;
24
25/**
26 * Tests {@link java.util.List#hashCode}.
27 *
28 * @author George van den Driessche
29 */
30@GwtCompatible(emulated = true)
31public class ListHashCodeTester<E> extends AbstractListTester<E> {
32  public void testHashCode() {
33    int expectedHashCode = 1;
34    for (E element : getOrderedElements()) {
35      expectedHashCode = 31 * expectedHashCode +
36          ((element == null) ? 0 : element.hashCode());
37    }
38    assertEquals(
39        "A List's hashCode() should be computed from those of its elements.",
40        expectedHashCode, getList().hashCode());
41  }
42
43  /**
44   * Returns the {@link Method} instance for {@link #testHashCode()} so that
45   * list tests on unhashable objects can suppress it with
46   * {@code FeatureSpecificTestSuiteBuilder.suppressing()}.
47   */
48  @GwtIncompatible("reflection")
49  public static Method getHashCodeMethod() {
50    return Helpers.getMethod(ListHashCodeTester.class, "testHashCode");
51  }
52}
53