Java

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/*
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 * Copyright (C) 2007 The Guava Authors
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 *
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 * Licensed under the Apache License, Version 2.0 (the "License");
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 * you may not use this file except in compliance with the License.
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 * You may obtain a copy of the License at
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 *
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 * http://www.apache.org/licenses/LICENSE-2.0
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 *
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 * Unless required by applicable law or agreed to in writing, software
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 * distributed under the License is distributed on an "AS IS" BASIS,
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 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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 * See the License for the specific language governing permissions and
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 * limitations under the License.
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 */
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package com.google.common.testing;
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import static com.google.common.base.Preconditions.checkNotNull;
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import static junit.framework.Assert.assertEquals;
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import static junit.framework.Assert.assertTrue;
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import com.google.common.annotations.GwtCompatible;
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import com.google.common.base.Equivalence;
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import com.google.common.collect.Iterables;
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import com.google.common.collect.Lists;
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import com.google.errorprone.annotations.CanIgnoreReturnValue;
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import java.util.ArrayList;
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import java.util.List;
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import org.checkerframework.checker.nullness.qual.Nullable;
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/**
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 * Tester for equals() and hashCode() methods of a class.
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 *
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 * <p>The simplest use case is:
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 *
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 * <pre>
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 * new EqualsTester().addEqualityGroup(foo).testEquals();
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 * </pre>
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 *
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 * <p>This tests {@code foo.equals(foo)}, {@code foo.equals(null)}, and a few other operations.
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 *
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 * <p>For more extensive testing, add multiple equality groups. Each group should contain objects
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 * that are equal to each other but unequal to the objects in any other group. For example:
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 *
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 * <pre>
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 * new EqualsTester()
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 *     .addEqualityGroup(new User("page"), new User("page"))
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 *     .addEqualityGroup(new User("sergey"))
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 *     .testEquals();
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 * </pre>
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 *
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 * <p>This tests:
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 *
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 * <ul>
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 *   <li>comparing each object against itself returns true
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 *   <li>comparing each object against null returns false
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 *   <li>comparing each object against an instance of an incompatible class returns false
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 *   <li>comparing each pair of objects within the same equality group returns true
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 *   <li>comparing each pair of objects from different equality groups returns false
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 *   <li>the hash codes of any two equal objects are equal
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 * </ul>
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 *
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 * <p>When a test fails, the error message labels the objects involved in the failed comparison as
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 * follows:
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 *
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 * <ul>
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 *   <li>"{@code [group }<i>i</i>{@code , item }<i>j</i>{@code ]}" refers to the
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 *       <i>j</i><sup>th</sup> item in the <i>i</i><sup>th</sup> equality group, where both equality
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 *       groups and the items within equality groups are numbered starting from 1. When either a
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 *       constructor argument or an equal object is provided, that becomes group 1.
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 * </ul>
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 *
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 * @author Jim McMaster
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 * @author Jige Yu
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 * @since 10.0
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 */
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@GwtCompatible
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@ElementTypesAreNonnullByDefault
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public final class EqualsTester {
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  private static final int REPETITIONS = 3;
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  private final List<List<Object>> equalityGroups = Lists.newArrayList();
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  private final RelationshipTester.ItemReporter itemReporter;
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  /** Constructs an empty EqualsTester instance */
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  public EqualsTester() {
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    this(new RelationshipTester.ItemReporter());
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  }
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  EqualsTester(RelationshipTester.ItemReporter itemReporter) {
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    this.itemReporter = checkNotNull(itemReporter);
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  }
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  /**
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   * Adds {@code equalityGroup} with objects that are supposed to be equal to each other and not
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   * equal to any other equality groups added to this tester.
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   *
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   * <p>The {@code @Nullable} annotations on the {@code equalityGroup} parameter imply that the
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   * objects, and the array itself, can be null. That is for programmer convenience, when the
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   * objects come from factory methods that are themselves {@code @Nullable}. In reality neither the
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   * array nor its contents can be null, but it is not useful to force the use of {@code
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   * requireNonNull} or the like just to assert that.
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   *
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   * <p>{@code EqualsTester} will always check that every object it is given returns false from
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   * {@code equals(null)}, so it is neither useful nor allowed to include a null value in any
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   * equality group.
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   */
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  @CanIgnoreReturnValue
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  public EqualsTester addEqualityGroup(@Nullable Object @Nullable ... equalityGroup) {
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    checkNotNull(equalityGroup);
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    List<Object> list = new ArrayList<>(equalityGroup.length);
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    for (int i = 0; i < equalityGroup.length; i++) {
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      Object element = equalityGroup[i];
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      if (element == null) {
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        throw new NullPointerException("at index " + i);
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      }
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      list.add(element);
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    }
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    equalityGroups.add(list);
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    return this;
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  }
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  /** Run tests on equals method, throwing a failure on an invalid test */
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  @CanIgnoreReturnValue
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  public EqualsTester testEquals() {
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    RelationshipTester<Object> delegate =
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        new RelationshipTester<>(
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            Equivalence.equals(), "Object#equals", "Object#hashCode", itemReporter);
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    for (List<Object> group : equalityGroups) {
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      delegate.addRelatedGroup(group);
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    }
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    for (int run = 0; run < REPETITIONS; run++) {
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      testItems();
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      delegate.test();
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    }
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    return this;
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  }
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  private void testItems() {
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    for (Object item : Iterables.concat(equalityGroups)) {
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      assertTrue(item + " must not be Object#equals to null", !item.equals(null));
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      assertTrue(
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          item + " must not be Object#equals to an arbitrary object of another class",
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          !item.equals(NotAnInstance.EQUAL_TO_NOTHING));
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      assertTrue(item + " must be Object#equals to itself", item.equals(item));
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      assertEquals(
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          "the Object#hashCode of " + item + " must be consistent",
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          item.hashCode(),
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          item.hashCode());
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      if (!(item instanceof String)) {
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        assertTrue(
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            item + " must not be Object#equals to its Object#toString representation",
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            !item.equals(item.toString()));
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      }
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    }
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  }
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  /**
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   * Class used to test whether equals() correctly handles an instance of an incompatible class.
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   * Since it is a private inner class, the invoker can never pass in an instance to the tester
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   */
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  private enum NotAnInstance {
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    EQUAL_TO_NOTHING;
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  }
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}
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