*     source-compatible</a> since 4.0)
 */
@GwtCompatible
/*
 * The type parameter is <T> rather than <T extends @Nullable> so that we can use T in the
 * doEquivalent and doHash methods to indicate that the parameter cannot be null.
 */
@SuppressWarnings("UngroupedOverloads")
public abstract class Equivalence<T> implements BiPredicate<@Nullable T, @Nullable T> {

    if (a == b) {
      return true;
    }
    if (a == null || b == null) {
      return false;
    }
    return doEquivalent(a, b);
  }

  /**
   * @since 10.0 (previously, subclasses would override equivalent())
   */
  @ForOverride
  protected abstract boolean doEquivalent(T a, T b);

  /**
   * <i>May</i> return {@code true} if {@code object} is a {@code Equivalence} that behaves

    this.function = checkNotNull(function);
    this.resultEquivalence = checkNotNull(resultEquivalence);
  }

  @Override
  protected boolean doEquivalent(F a, F b) {
    return resultEquivalence.equivalent(function.apply(a), function.apply(b));
  }

  @Override
  protected int doHash(F a) {
    return resultEquivalence.hash(function.apply(a));
  }

  PairwiseEquivalence(Equivalence<E> elementEquivalence) {
    this.elementEquivalence = Preconditions.checkNotNull(elementEquivalence);
  }

  @Override
  protected boolean doEquivalent(Iterable<T> iterableA, Iterable<T> iterableB) {
    Iterator<T> iteratorA = iterableA.iterator();
    Iterator<T> iteratorB = iterableB.iterator();

    while (iteratorA.hasNext() && iteratorB.hasNext()) {

  PairwiseEquivalence(Equivalence<E> elementEquivalence) {
    this.elementEquivalence = Preconditions.checkNotNull(elementEquivalence);
  }

  @Override
  protected boolean doEquivalent(Iterable<T> iterableA, Iterable<T> iterableB) {
    Iterator<T> iteratorA = iterableA.iterator();
    Iterator<T> iteratorB = iterableB.iterator();

    while (iteratorA.hasNext() && iteratorB.hasNext()) {

    this.function = checkNotNull(function);
    this.resultEquivalence = checkNotNull(resultEquivalence);
  }

  @Override
  protected boolean doEquivalent(F a, F b) {
    return resultEquivalence.equivalent(function.apply(a), function.apply(b));
  }

  @Override
  protected int doHash(F a) {
    return resultEquivalence.hash(function.apply(a));
  }

      checkRecording();
      equivalentExpectations = equivalentExpectationsBuilder.buildOrThrow();
      hashExpectations = hashExpectationsBuilder.buildOrThrow();
    }

    @Override
    protected boolean doEquivalent(Object a, Object b) {
      return equivalentExpectations.get(a, b);
    }

    @Override
    protected int doHash(Object object) {
      return hashExpectations.get(object);
    }

      checkRecording();
      equivalentExpectations = equivalentExpectationsBuilder.buildOrThrow();
      hashExpectations = hashExpectationsBuilder.buildOrThrow();
    }

    @Override
    protected boolean doEquivalent(Object a, Object b) {
      return equivalentExpectations.get(a, b);
    }

    @Override
    protected int doHash(Object object) {
      return hashExpectations.get(object);
    }

    return Splitter.on(generateString());
  }

  @Generates
  <T> Equivalence<T> generateEquivalence() {
    return new Equivalence<T>() {
      @Override
      protected boolean doEquivalent(T a, T b) {
        return false;
      }

      @Override
      protected int doHash(T t) {
        return 0;
      }

      final String string = paramString(Equivalence.class, generateInt());

    return Splitter.on(generateString());
  }

  @Generates
  <T> Equivalence<T> generateEquivalence() {
    return new Equivalence<T>() {
      @Override
      protected boolean doEquivalent(T a, T b) {
        return false;
      }

      @Override
      protected int doHash(T t) {
        return 0;
      }

      final String string = paramString(Equivalence.class, generateInt());