Iterators.java revision 2973:0e8fa3249327 
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 */
25package com.sun.tools.javac.util;
26
27import java.util.Iterator;
28import java.util.NoSuchElementException;
29import 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 */
38public 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}
74