Added an implemention of ArrayDeque, as well as unit tests

I also used this opportunity to reduce code duplication around other queue/deque implementations.

classpath/java/util/concurrent/ConcurrentLinkedQueue.java

@@ -1,13 +1,12 @@
 package java.util.concurrent;
 
+import java.util.AbstractQueue;
 import java.util.Collection;
 import java.util.Iterator;
-import java.util.NoSuchElementException;
-import java.util.Queue;
 
 import avian.Atomic;
 
-public class ConcurrentLinkedQueue<T> implements Queue<T> {
+public class ConcurrentLinkedQueue<T> extends AbstractQueue<T> {
   private static final long QueueHead;
   private static final long QueueTail;
   private static final long NodeNext;
@@ -67,31 +66,11 @@ public class ConcurrentLinkedQueue<T> implements Queue<T> {
     return poll(false);
   }
 
-  @Override
-  public T element() {
-    T result = peek();
-    if (result == null) {
-      throw new NoSuchElementException();
-    } else {
-      return result;
-    }
-  }
-
   @Override
   public T poll() {
     return poll(true);
   }
 
-  @Override
-  public T remove() {
-    T result = poll();
-    if (result == null) {
-      throw new NoSuchElementException();
-    } else {
-      return result;
-    }
-  }
-
   private T poll(boolean remove) {
     while (true) {
       Node<T> h = head;
@@ -150,12 +129,6 @@ public class ConcurrentLinkedQueue<T> implements Queue<T> {
     throw new UnsupportedOperationException();
   }
 
-  @Override
-  public boolean addAll(Collection<? extends T> collection) {
-    // TODO - implement
-    throw new UnsupportedOperationException();
-  }
-
   @Override
   public boolean remove(Object element) {
     // TODO - implement