--- jsr166/src/main/java/util/AbstractQueue.java	2003/05/18 18:10:02	1.1
+++ jsr166/src/main/java/util/AbstractQueue.java	2003/09/13 22:28:58	1.17
@@ -1,21 +1,71 @@
+/*
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain. Use, modify, and
+ * redistribute this code in any way without acknowledgement.
+ */
+
 package java.util;
 
 /**
- * AbstractQueue provides default implementations of add, remove, and
- * element based on offer, poll, and peek, respectively but that throw
- * exceptions instead of indicating failure via false or null returns.
- * The provided implementations all assume that the base implementation
- * does <em>not</em> allow null elements.
+ * This class provides skeletal implementations of some {@link Queue}
+ * operations. The implementations in this class are appropriate when
+ * the base implementation does <em>not</em> allow <tt>null</tt>
+ * elements.  Methods {@link #add add}, {@link #remove remove}, and
+ * {@link #element element} are based on {@link #offer offer}, {@link
+ * #poll poll}, and {@link #peek peek}, respectively but throw
+ * exceptions instead of indicating failure via <tt>false</tt> or
+ * <tt>null</tt> returns.
+ *
+ * <p> A <tt>Queue</tt> implementation that extends this class must
+ * minimally define a method {@link Queue#offer} which does not permit
+ * insertion of <tt>null</tt> elements, along with methods {@link
+ * Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and a
+ * {@link Collection#iterator} supporting {@link
+ * Iterator#remove}. Typically, additional methods will be overriden
+ * as well. If these requirements cannot be met, consider instead
+ * subclassing {@link AbstractCollection}.
+ *
+ * @since 1.5
+ * @author Doug Lea
  */
-public abstract class AbstractQueue<E> extends AbstractCollection<E> implements Queue<E> {
+public abstract class AbstractQueue<E>
+    extends AbstractCollection<E>
+    implements Queue<E> {
+
+    /**
+     * Constructor for use by subclasses.
+     */
+    protected AbstractQueue() {
+    }
 
-    public boolean add(E x) {
-        if (offer(x))
+
+    /**
+     * Adds the specified element to this queue. This implementation
+     * returns <tt>true</tt> if <tt>offer</tt> succeeds, else
+     * throws an IllegalStateException. 
+     * 
+     * @param o the element
+     * @return <tt>true</tt> (as per the general contract of
+     *         <tt>Collection.add</tt>).
+     *
+     * @throws NullPointerException if the specified element is <tt>null</tt>
+     * @throws IllegalStateException if element cannot be added
+     */
+    public boolean add(E o) {
+        if (offer(o))
             return true;
         else
             throw new IllegalStateException("Queue full");
     }
 
+    /**
+     * Retrieves and removes the head of this queue.
+     * This implementation returns the result of <tt>poll</tt>
+     * unless the queue is empty.
+     *
+     * @return the head of this queue.
+     * @throws NoSuchElementException if this queue is empty.
+     */
     public E remove() {
         E x = poll();
         if (x != null)
@@ -24,6 +74,15 @@ public abstract class AbstractQueue<E> e
             throw new NoSuchElementException();
     }
 
+
+    /**
+     * Retrieves, but does not remove, the head of this queue.  
+     * This implementation returns the result of <tt>peek</tt>
+     * unless the queue is empty.
+     *
+     * @return the head of this queue.
+     * @throws NoSuchElementException if this queue is empty.
+     */
     public E element() {
         E x = peek();
         if (x != null)
@@ -32,9 +91,14 @@ public abstract class AbstractQueue<E> e
             throw new NoSuchElementException();
     }
 
+    /**
+     * Removes all of the elements from this collection.
+     * The collection will be empty after this call returns.
+     * <p>This implementation repeatedly invokes {@link #poll poll} until it
+     * returns <tt>null</tt>.
+     */
     public void clear() {
         while (poll() != null)
             ;
     }
-
 }