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