src/java.base/share/classes/java/util/Enumeration.java

rev 11962 : 8072726: add adapter to convert Enumeration to Iterator
Reviewed-by: XXX

@@ -1,7 +1,7 @@
 /*
- * Copyright (c) 1994, 2005, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1994, 2015, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.  Oracle designates this

@@ -74,6 +74,61 @@
      *
      * @return     the next element of this enumeration.
      * @exception  NoSuchElementException  if no more elements exist.
      */
     E nextElement();
+
+    /**
+     * Returns an {@link Iterator} whose elements are the same as the
+     * elements of this {@code Enumeration}. The results are undefined
+     * if this method is called more than once, or if this Enumeration's
+     * other methods are called after {@code asIterator} has been called.
+     *
+     * @apiNote
+     * This method is intended to help adapt code that produces
+     * {@code Enumeration} instances to code that consumes {@code Iterator}
+     * or {@code Iterable} instances. For example, the
+     * {@link java.security.PermissionCollection PermissionCollection.elements()}
+     * method returns an {@code Enumeration<Permission>}. This can be adapted
+     * for use in an enhanced-for loop as follows:
+     *
+     * <pre>{@code
+     *     PermissionCollection pc = ... ;
+     *     Iterable<Permission> permsIterable = () -> pc.elements().asIterator();
+     *     for (Permission p : permsIterable) {
+     *         doSomethingWithPermission(p);
+     *     }
+     * }</pre>
+     *
+     * A {@code Stream<Permission>} could be created from an
+     * {@code Enumeration<Permission>} as follows:
+     *
+     * <pre>{@code
+     *     Stream<Permission> permsStream = StreamSupport.stream(
+     *         Spliterators.spliteratorUnknownSize(
+     *             pc.elements().asIterator(),
+     *             Spliterator.ORDERED | Spliterator.IMMUTABLE),
+     *         false);
+     * }</pre>
+     *
+     * @implSpec
+     * The returned Iterator's {@link Iterator#hasNext hasNext} method calls and returns
+     * the value from this Enumeration's {@code hasMoreElements} method; its
+     * {@link Iterator#next next} method calls and returns the value from this Enumeration's
+     * {@code nextElement} method; and its {@link Iterator#remove remove} method throws
+     * {@code UnsupportedOperationException}.
+     *
+     * @return an Iterator derived from this Enumeration
+     *
+     * @since 1.9
+     */
+    default Iterator<E> asIterator() {
+        return new Iterator<E>() {
+            @Override public boolean hasNext() {
+                return Enumeration.this.hasMoreElements();
+            }
+            @Override public E next() {
+                return Enumeration.this.nextElement();
+            }
+        };
+    }
 }