// See the note about volatile in the superclass.
  private transient volatile @Nullable CacheEntry<K, V> cacheEntry1;
  private transient volatile @Nullable CacheEntry<K, V> cacheEntry2;

  MapRetrievalCache(Map<K, V> backingMap) {
    super(backingMap);
  }

  @SuppressWarnings("unchecked") // Safe because we only cast if key is found in map.
  @Override
  @Nullable V get(Object key) {
    checkNotNull(key);
    V value = getIfCached(key);

 *       String}.
 * </ul>
 *
 * This is the same behavior as type-variable usages have to Kotlin and to the Checker Framework.
 * Contrast the method above to:
 *
 * <ul>
 *   <li>methods whose return type is a type variable but which can never return {@code null},
 *       typically because the type forbids nullable type arguments: For example, {@code

 *       String}.
 * </ul>
 *
 * This is the same behavior as type-variable usages have to Kotlin and to the Checker Framework.
 * Contrast the method above to:
 *
 * <ul>
 *   <li>methods whose return type is a type variable but which can never return {@code null},
 *       typically because the type forbids nullable type arguments: For example, {@code

 *       String}.
 * </ul>
 *
 * This is the same behavior as type-variable usages have to Kotlin and to the Checker Framework.
 * Contrast the method above to:
 *
 * <ul>
 *   <li>methods whose return type is a type variable but which can never return {@code null},
 *       typically because the type forbids nullable type arguments: For example, {@code

 *       String}.
 * </ul>
 *
 * This is the same behavior as type-variable usages have to Kotlin and to the Checker Framework.
 * Contrast the method above to:
 *
 * <ul>
 *   <li>methods whose return type is a type variable but which can never return {@code null},
 *       typically because the type forbids nullable type arguments: For example, {@code

import java.util.Map;
import org.jspecify.annotations.Nullable;

/**
 * An object representing the differences between two maps.
 *
 * @author Kevin Bourrillion
 * @since 2.0
 */
@DoNotMock("Use Maps.difference")
@GwtCompatible
public interface MapDifference<K extends @Nullable Object, V extends @Nullable Object> {
  /**

import java.util.List;
import java.util.Map.Entry;
import org.jspecify.annotations.NullMarked;
import org.jspecify.annotations.Nullable;

/**
 * A container class for the five sample elements we need for testing.
 *
 * @author Kevin Bourrillion
 */
@GwtCompatible
@NullMarked
public class SampleElements<E extends @Nullable Object> implements Iterable<E> {
  // TODO: rename e3, e4 => missing1, missing2
  private final E e0;

   * a very fast escape method.
   */
  private static final class CharArrayDecorator extends CharEscaper {
    private final char[] @Nullable [] replacements;
    private final int replaceLength;

    CharArrayDecorator(char[] @Nullable [] replacements) {
      this.replacements = replacements;
      this.replaceLength = replacements.length;
    }

    /*

   * PeekingIterator#remove()} removes the same elements as the reference's iterator {@code
   * remove()}.
   */
  private static class PeekingIteratorTester<T extends @Nullable Object> extends IteratorTester<T> {
    private final Iterable<T> master;
    private @Nullable List<T> targetList;

    PeekingIteratorTester(Collection<T> master) {
      super(master.size() + 3, MODIFIABLE, master, IteratorTester.KnownOrder.KNOWN_ORDER);

import java.util.Map.Entry;
import java.util.Set;
import org.jspecify.annotations.Nullable;

/**
 * Implementation of {@link Multimaps#filterKeys(SetMultimap, Predicate)}.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
final class FilteredKeySetMultimap<K extends @Nullable Object, V extends @Nullable Object>
    extends FilteredKeyMultimap<K, V> implements FilteredSetMultimap<K, V> {