1 /*
   2  * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 package java.lang;
  26 
  27 import java.util.Iterator;
  28 
  29 /**
  30  * An Iterable from which only a single Iterator can be obtained.
  31  *
  32  * @apiNote
  33  * IterableOnce is functionally identical to Iterable. A class can
  34  * implement IterableOnce in preference to Iterable in order to signal
  35  * to applications that only a single Iterator can be obtained. It is
  36  * recommended that attempts to call the iterator() method the second
  37  * and subsequent time results in IllegalStateException.
  38  *
  39  * @param <T> the type of elements returned by the iterator
  40  */
  41 public interface IterableOnce<T> extends Iterable<T> {
  42     /**
  43      * Returns an iterator over elements of type {@code T}. This method
  44      * can be called successfully only once. The second and subsequent
  45      * invocations of this method throw IllegalStateException.
  46      *
  47      * @return an Iterator
  48      * @throws IllegalStateException if this method has been called previously
  49      */
  50     Iterator<T> iterator();
  51 }