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