1 /*
   2  * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  *
   8  *   - Redistributions of source code must retain the above copyright
   9  *     notice, this list of conditions and the following disclaimer.
  10  *
  11  *   - Redistributions in binary form must reproduce the above copyright
  12  *     notice, this list of conditions and the following disclaimer in the
  13  *     documentation and/or other materials provided with the distribution.
  14  *
  15  *   - Neither the name of Oracle nor the names of its
  16  *     contributors may be used to endorse or promote products derived
  17  *     from this software without specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
  20  * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  21  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
  23  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  24  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  25  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  26  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
  27  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  28  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  29  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  30  */
  31 
  32 import java.util.Iterator;
  33 import java.util.NoSuchElementException;
  34 
  35 /**
  36  * The code sample illustrates the usage of default methods in the JDK 8. Most
  37  * implementations of Iterator don’t provide a useful remove() method, however, 
  38  * they still have to implement this method to throw 
  39  * an UnsupportedOperationException. With the default method, the same
  40  * default behavior in interface Iterator itself can be provided.
  41  *
  42  * @author Taras Ledkov
  43  */
  44 public class ArrayIterator {
  45 
  46     /** Close the constructor because ArrayIterator is part of the utility 
  47      * class.
  48      */
  49     protected ArrayIterator() {
  50         throw new UnsupportedOperationException();
  51     }
  52 
  53     /**
  54      * Returns an iterator that goes over the elements in the array.
  55      *
  56      * @param <E> type of an array element
  57      * @param array source array to iterate over it
  58      * @return an iterator that goes over the elements in the array
  59      */
  60     public static <E> Iterator<E> iterator(final E[] array) {
  61         return new Iterator<E>() {
  62             /**
  63              * Initial array
  64              *
  65              */
  66             private final E[] srcArray = array;
  67 
  68             /**
  69              * Index of the current position
  70              *
  71              */
  72             private int index = 0;
  73 
  74             /**
  75              * Returns the next element in the iteration
  76              *
  77              * @return the next element in the iteration
  78              * @throws NoSuchElementException if the iteration has no more
  79              * elements
  80              */
  81             @Override
  82             public boolean hasNext() {
  83                 return (index < srcArray.length);
  84             }
  85 
  86             /**
  87              * Returns {@code true} if the iteration has more elements. (In
  88              * other words, returns {@code true} if {@link #next} returns
  89              * an element, rather than throwing an exception.)
  90              *
  91              * @return {@code true} if the iteration has more elements
  92              */
  93             @Override
  94             public E next() {
  95                 if (!hasNext()) {
  96                     throw new NoSuchElementException();
  97                 }
  98                 return srcArray[index++];
  99             }
 100 
 101             /**
 102              * This method does not need to be overwritten in JDK 8.
 103              */
 104             //@Override
 105             //public void remove() {
 106             //    throw UnsupportedOperationException(
 107             //            "Arrays don't support remove.")
 108             //}
 109         };
 110     }
 111 
 112     /**
 113      * Sample usage of the ArrayIterator
 114      *
 115      * @param args command-line arguments
 116      */
 117     public static void main(final String[] args) {
 118         Iterator<String> it = ArrayIterator.iterator(
 119                 new String[]{"one", "two", "three"});
 120 
 121         while (it.hasNext()) {
 122             System.out.println(it.next());
 123         }
 124     }
 125 }