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  
17  package com.google.common.collect.testing.testers;
18  
19  import com.google.common.annotations.GwtCompatible;
20  import com.google.common.annotations.GwtIncompatible;
21  import com.google.common.collect.testing.Helpers;
22  
23  import 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)
31  public 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  }