public Deque<?> apply(Deque delegate) {
                return wrap((Deque<?>) delegate);
              }
            });
  }

  private static <T> Deque<T> wrap(final Deque<T> delegate) {
    return new ForwardingDeque<T>() {
      @Override
      protected Deque<T> delegate() {
        return delegate;
      }
    };
  }

              public Deque<?> apply(Deque delegate) {
                return wrap((Deque<?>) delegate);
              }
            });
  }

  private static <T> Deque<T> wrap(final Deque<T> delegate) {
    return new ForwardingDeque<T>() {
      @Override
      protected Deque<T> delegate() {
        return delegate;
      }
    };
  }

import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Deque;
import java.util.Iterator;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * A deque which forwards all its method calls to another deque. Subclasses should override one or
 * more methods to modify the behavior of the backing deque as desired per the <a

   *
   * @param deque the deque to be wrapped in a synchronized view
   * @return a synchronized view of the specified deque
   * @since 15.0
   */
  public static <E extends @Nullable Object> Deque<E> synchronizedDeque(Deque<E> deque) {
    return Synchronized.deque(deque, null);
  }

     */
    @CheckForNull
    abstract N visitNext(Deque<Iterator<? extends N>> horizon);
  }

  /** Poor man's method reference for {@code Deque::addFirst} and {@code Deque::addLast}. */
  private enum InsertionOrder {
    FRONT {
      @Override
      <T> void insertInto(Deque<T> deque, T value) {
        deque.addFirst(value);
      }
    },
    BACK {
      @Override

import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Queues;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;
import java.util.Deque;
import java.util.Map;
import java.util.concurrent.Executor;
import java.util.concurrent.Future;
import java.util.concurrent.atomic.AtomicInteger;
import junit.framework.TestCase;

/**

    Deque<String> outer = Synchronized.deque(inner, inner.mutex);
    outer.add("foo"); // necessary because we try to remove elements later on
    return outer;
  }

  private static final class TestDeque<E> implements Deque<E> {
    private final Deque<E> delegate = Lists.newLinkedList();
    public final Object mutex = new Integer(1); // something Serializable

    @Override
    public boolean offer(E o) {

  }

  static <E extends @Nullable Object> Deque<E> deque(Deque<E> deque, @CheckForNull Object mutex) {
    return new SynchronizedDeque<>(deque, mutex);
  }

  static final class SynchronizedDeque<E extends @Nullable Object> extends SynchronizedQueue<E>
      implements Deque<E> {

    SynchronizedDeque(Deque<E> delegate, @CheckForNull Object mutex) {
      super(delegate, mutex);
    }

import java.nio.ShortBuffer;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.BitSet;
import java.util.Collection;
import java.util.Comparator;
import java.util.Currency;
import java.util.Deque;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
import java.util.Locale;
import java.util.Map;

import com.google.errorprone.annotations.concurrent.GuardedBy;
import com.google.errorprone.annotations.concurrent.LazyInit;
import com.google.j2objc.annotations.RetainedWith;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.concurrent.Executor;
import java.util.concurrent.RejectedExecutionException;
import java.util.logging.Level;
import javax.annotation.CheckForNull;

/**