@Override
    public boolean equals(@Nullable Object other) {
      return (other instanceof ClassWhichIsAlwaysEqualButHasDifferentHashcodes);
    }
  }

  private static class ObjectWhichIsEqualButChangesClass implements Serializable {
    private static final long serialVersionUID = 1L;

    @Override
    public boolean equals(@Nullable Object other) {

import junit.framework.TestCase;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Tests for {@link Multisets#immutableEntry}.
 *
 * @author Mike Bostock
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public class MultisetsImmutableEntryTest extends TestCase {
  private static final @Nullable String NE = null;

  private static <E extends @Nullable Object> Entry<E> entry(final E element, final int count) {

    List<@Nullable String> listWithNulls = asList("a", null, "b");
      assertThrows(NullPointerException.class, () -> builder.addAll((List<String>) listWithNulls));
    }

    {
      ImmutableList.Builder<String> builder = ImmutableList.builder();
    Iterator<@Nullable String> iteratorWithNulls =
        Arrays.<@Nullable String>asList("a", null, "b").iterator();
      assertThrows(

import org.checkerframework.checker.nullness.qual.Nullable;
import org.junit.Ignore;

/** Skeleton for a tester of a {@code BiMap}. */
@GwtCompatible
@Ignore // Affects only Android test runner, which respects JUnit 4 annotations on JUnit 3 tests.
@SuppressWarnings("JUnit4ClassUsedInJUnit3")
@ElementTypesAreNonnullByDefault
public abstract class AbstractBiMapTester<K extends @Nullable Object, V extends @Nullable Object>
    extends AbstractMapTester<K, V> {

import java.util.Map.Entry;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Creates bimaps, containing sample entries, to be tested.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public interface TestBiMapGenerator<K extends @Nullable Object, V extends @Nullable Object>
    extends TestContainerGenerator<BiMap<K, V>, Entry<K, V>> {

import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Implementation of {@link Multimaps#filterEntries(Multimap, Predicate)}.
 *
 * @author Jared Levy
 * @author Louis Wasserman
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
class FilteredEntryMultimap<K extends @Nullable Object, V extends @Nullable Object>
    extends AbstractMultimap<K, V> implements FilteredMultimap<K, V> {

      return standardSubMultiset(lowerBound, lowerBoundType, upperBound, upperBoundType);
    }

    @Override
    public int count(@Nullable Object element) {
      return standardCount(element);
    }

    @Override
    public boolean equals(@Nullable Object object) {
      return standardEquals(object);
    }

    @Override
    public int hashCode() {
      return standardHashCode();
    }

    multimap.put("bar", 9);
    assertThat(multimap.keySet()).containsExactly("cow", "bar").inOrder();
  }

  public void testToStringNullExact() {
    Multimap<@Nullable String, @Nullable Integer> multimap = LinkedHashMultimap.create();

    multimap.put("foo", 3);
    multimap.put("foo", -1);
    multimap.put(null, null);
    multimap.put("bar", 1);
    multimap.put("foo", 2);

import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.NoSuchElementException;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Basic implementation of {@code Multiset<E>} backed by an instance of {@code
 * ObjectCountHashMap<E>}.
 *
 * <p>For serialization to work, the subclass must specify explicit {@code readObject} and {@code

   * href="http://gee.cs.oswego.edu/dl/html/StreamParallelGuidance.html">efficiently splittable</a>.
   * This may harm parallel performance.
   */
  @Beta
  public static <A extends @Nullable Object, B extends @Nullable Object, R extends @Nullable Object>
      Stream<R> zip(
          Stream<A> streamA, Stream<B> streamB, BiFunction<? super A, ? super B, R> function) {
    checkNotNull(streamA);
    checkNotNull(streamB);