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 /** Utilities for Iterators.

    32  *

    33  *  <p><b>This is NOT part of any supported API.

    34  *  If you write code that depends on this, you do so at your own risk.

    35  *  This code and its internal interfaces are subject to change or

    36  *  deletion without notice.</b>

    37  */

    38 public class Iterators {

    39 

    40     public static <I, O> Iterator<O> createCompoundIterator(Iterable<I> inputs, Function<I, Iterator<O>> convertor) {

    41         return new CompoundIterator<>(inputs, convertor);

    42     }

    43 

    44     private static class CompoundIterator<I, O> implements Iterator<O> {

    45 

    46         private final Iterator<I> inputs;

    47         private final Function<I, Iterator<O>> convertor;

    48         private Iterator<O> currentIterator;

    49 

    50         public CompoundIterator(Iterable<I> inputs, Function<I, Iterator<O>> convertor) {

    51             this.inputs = inputs.iterator();

    52             this.convertor = convertor;

    53         }

    54 

    55         public boolean hasNext() {

    56             while (inputs.hasNext() && (currentIterator == null || !currentIterator.hasNext())) {

    57                 currentIterator = convertor.apply(inputs.next());

    58             }

    59             return currentIterator != null && currentIterator.hasNext();

    60         }

    61 

    62         public O next() {

    63             if (!hasNext())

    64                 throw new NoSuchElementException();

    65 

    66             return currentIterator.next();

    67         }

    68 

    69         public void remove() {

    70             throw new UnsupportedOperationException();

    71         }

    72     }

    73 }