* ForwardingNavigableMap#navigableKeySet} to forward to this implementation or a subclass
   * thereof.
   *
   * @since 12.0
   */
  protected class StandardNavigableKeySet extends Maps.NavigableKeySet<K, V> {
    /** Constructor for use by subclasses. */
    public StandardNavigableKeySet() {
      super(ForwardingNavigableMap.this);
    }
  }

  @Override

   * ForwardingNavigableMap#navigableKeySet} to forward to this implementation or a subclass
   * thereof.
   *
   * @since 12.0
   */
  protected class StandardNavigableKeySet extends Maps.NavigableKeySet<K, V> {
    /** Constructor for use by subclasses. */
    public StandardNavigableKeySet() {
      super(ForwardingNavigableMap.this);
    }
  }

  @Override

import java.util.Iterator;
import java.util.Map.Entry;
import java.util.SortedMap;

/**
 * Tests representing the contract of {@link SortedMap}. Concrete subclasses of this base class test
 * conformance of concrete {@link SortedMap} subclasses to that contract.
 *
 * @author Jared Levy
 */
// TODO: Use this class to test classes besides ImmutableSortedMap.
@GwtCompatible

import java.util.Iterator;
import java.util.Map.Entry;
import java.util.SortedMap;

/**
 * Tests representing the contract of {@link SortedMap}. Concrete subclasses of this base class test
 * conformance of concrete {@link SortedMap} subclasses to that contract.
 *
 * @author Jared Levy
 */
// TODO: Use this class to test classes besides ImmutableSortedMap.
@GwtCompatible

import java.util.concurrent.TimeUnit;
import org.jspecify.annotations.Nullable;

/**
 * A {@link BlockingDeque} which forwards all its method calls to another {@code BlockingDeque}.
 * Subclasses should override one or more methods to modify the behavior of the backing deque as
 * desired per the <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *

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

/**
 * A multimap which forwards all its method calls to another multimap. Subclasses should override
 * one or more methods to modify the behavior of the backing multimap as desired per the <a
 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *

import com.google.common.annotations.GwtCompatible;
import java.util.Collection;
import java.util.Set;
import org.jspecify.annotations.Nullable;

/**
 * A set which forwards all its method calls to another set. Subclasses should override one or more
 * methods to modify the behavior of the backing set as desired per the <a
 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *

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

/**
 * A multimap which forwards all its method calls to another multimap. Subclasses should override
 * one or more methods to modify the behavior of the backing multimap as desired per the <a
 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *

 *
 * @author Jared Levy
 * @since 2.0
 */
@GwtCompatible
public abstract class UnmodifiableIterator<E extends @Nullable Object> implements Iterator<E> {
  /** Constructor for use by subclasses. */
  protected UnmodifiableIterator() {}

  /**
   * Guaranteed to throw an exception and leave the underlying data unmodified.
   *
   * @throws UnsupportedOperationException always

import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import org.jspecify.annotations.Nullable;

/**
 * An abstract {@code ExecutorService} that allows subclasses to {@linkplain #wrapTask(Callable)
 * wrap} tasks before they are submitted to the underlying executor.
 *
 * <p>Note that task wrapping may occur even if the task is never executed.
 *