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 java.lang.reflect.Method;
20
21/**
22 * Tests {@link java.util.List#hashCode}.
23 *
24 * <p>This class is GWT compatible.
25 *
26 * @author George van den Driessche
27 */
28public class ListHashCodeTester<E> extends AbstractListTester<E> {
29  public void testHashCode() {
30    int expectedHashCode = 1;
31    for (E element : getSampleElements()) {
32      expectedHashCode = 31 * expectedHashCode +
33          ((element == null) ? 0 : element.hashCode());
34    }
35    assertEquals(
36        "A List's hashCode() should be computed from those of its elements.",
37        expectedHashCode, getList().hashCode());
38  }
39
40  /**
41   * Returns the {@link Method} instance for {@link #testHashCode()} so that
42   * list tests on unhashable objects can suppress it with
43   * {@code FeatureSpecificTestSuiteBuilder.suppressing()}.
44   */
45  public static Method getHashCodeMethod() {
46    return Platform.getMethod(ListHashCodeTester.class, "testHashCode");
47  }
48}
49