1 /*
   2  * Copyright (c) 2015, 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 com.sun.tools.javac.util;
  26 
  27 import java.util.Iterator;
  28 import java.util.NoSuchElementException;
  29 import java.util.function.Function;
  30 
  31 public class Iterators {
  32 
  33     public static <I, O> Iterator<O> createCompoundIterator(Iterable<I> inputs, Function<I, Iterator<O>> convertor) {
  34         return new CompoundIterator<>(inputs, convertor);
  35     }
  36 
  37     private static class CompoundIterator<I, O> implements Iterator<O> {
  38 
  39         private final Iterator<I> inputs;
  40         private final Function<I, Iterator<O>> convertor;
  41         private Iterator<O> currentIterator;
  42 
  43         public CompoundIterator(Iterable<I> inputs, Function<I, Iterator<O>> convertor) {
  44             this.inputs = inputs.iterator();
  45             this.convertor = convertor;
  46         }
  47 
  48         public boolean hasNext() {
  49             while (inputs.hasNext() && (currentIterator == null || !currentIterator.hasNext())) {
  50                 currentIterator = convertor.apply(inputs.next());
  51             }
  52             return currentIterator != null && currentIterator.hasNext();
  53         }
  54 
  55         public O next() {
  56             if (!hasNext())
  57                 throw new NoSuchElementException();
  58 
  59             return currentIterator.next();
  60         }
  61 
  62         public void remove() {
  63             throw new UnsupportedOperationException();
  64         }
  65     }
  66 }