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

rev 11962 : 8072726: add adapter to convert Enumeration to Iterator
Reviewed-by: redestad, forax, chegar, dfuchs, psandoz

*** 1,7 ****
  /*
!  * Copyright (c) 1994, 2005, 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
--- 1,7 ----
  /*
!  * 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
*** 38,52 ****
   * <p>
   * Methods are provided to enumerate through the elements of a
   * vector, the keys of a hashtable, and the values in a hashtable.
   * Enumerations are also used to specify the input streams to a
   * <code>SequenceInputStream</code>.
!  * <p>
!  * NOTE: The functionality of this interface is duplicated by the Iterator
!  * interface.  In addition, Iterator adds an optional remove operation, and
!  * has shorter method names.  New implementations should consider using
!  * Iterator in preference to Enumeration.
   *
   * @see     java.util.Iterator
   * @see     java.io.SequenceInputStream
   * @see     java.util.Enumeration#nextElement()
   * @see     java.util.Hashtable
--- 38,55 ----
   * <p>
   * Methods are provided to enumerate through the elements of a
   * vector, the keys of a hashtable, and the values in a hashtable.
   * Enumerations are also used to specify the input streams to a
   * <code>SequenceInputStream</code>.
!  * 
!  * @apiNote
!  * The functionality of this interface is duplicated by the {@link Iterator}
!  * interface.  In addition, {@code Iterator} adds an optional remove operation,
!  * and has shorter method names.  New implementations should consider using
!  * {@code Iterator} in preference to {@code Enumeration}. It is possible to
!  * adapt an {@code Enumeration} to an {@code Iterator} by using the
!  * {@link #asIterator} method.
   *
   * @see     java.util.Iterator
   * @see     java.io.SequenceInputStream
   * @see     java.util.Enumeration#nextElement()
   * @see     java.util.Hashtable
*** 74,79 ****
--- 77,129 ----
       *
       * @return     the next element of this enumeration.
       * @exception  NoSuchElementException  if no more elements exist.
       */
      E nextElement();
+ 
+     /**
+      * Returns an {@link Iterator} that traverses the remaining elements
+      * covered by this enumeration. Traversal is undefined if any methods
+      * are called on this enumeration after the call to {@code asIterator}.
+      *
+      * @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.util.jar.JarFile#entries JarFile.entries()}
+      * method returns an {@code Enumeration<JarEntry>}. This can be adapted
+      * for use in an enhanced-for loop as follows:
+      *
+      * <pre>{@code
+      *     JarFile jf = ... ;
+      *     Iterable<JarEntry> entries = () -> jf.entries().asIterator();
+      *     for (JarEntry je : entries) {
+      *         doSomethingWithEntry(je);
+      *     }
+      * }</pre>
+      * 
+      * Note that the lambda expression being used as an {@code Iterable}
+      * fetches a new {@code Enumeration} each time, so that the resulting
+      * {@code Iterator} instances do not interfere with each other.
+      *
+      * @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 representing the remaining elements of this Enumeration
+      *
+      * @since 1.9
+      */
+     default Iterator<E> asIterator() {
+         return new Iterator<>() {
+             @Override public boolean hasNext() {
+                 return hasMoreElements();
+             }
+             @Override public E next() {
+                 return nextElement();
+             }
+         };
+     }
  }