Iterators.java revision 3681:076a0354bedb 
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
26package com.sun.tools.javac.util;
27
28import java.util.Iterator;
29import java.util.NoSuchElementException;
30import java.util.function.Function;
31
32/** Utilities for Iterators.
33 *
34 *  <p><b>This is NOT part of any supported API.
35 *  If you write code that depends on this, you do so at your own risk.
36 *  This code and its internal interfaces are subject to change or
37 *  deletion without notice.</b>
38 */
39public class Iterators {
40
41    public static <I, O> Iterator<O> createCompoundIterator(Iterable<I> inputs, Function<I, Iterator<O>> convertor) {
42        return new CompoundIterator<>(inputs, convertor);
43    }
44
45    private static class CompoundIterator<I, O> implements Iterator<O> {
46
47        private final Iterator<I> inputs;
48        private final Function<I, Iterator<O>> convertor;
49        @SuppressWarnings("unchecked")
50        private Iterator<O> currentIterator = EMPTY;
51
52        public CompoundIterator(Iterable<I> inputs, Function<I, Iterator<O>> convertor) {
53            this.inputs = inputs.iterator();
54            this.convertor = convertor;
55        }
56
57        public boolean hasNext() {
58            if (currentIterator != null && !currentIterator.hasNext()) {
59                update();
60            }
61            return currentIterator != null;
62        }
63
64        public O next() {
65            if (!hasNext())
66                throw new NoSuchElementException();
67
68            return currentIterator.next();
69        }
70
71        public void remove() {
72            throw new UnsupportedOperationException();
73        }
74
75        private void update() {
76            while (inputs.hasNext()) {
77                currentIterator = convertor.apply(inputs.next());
78                if (currentIterator.hasNext()) return;
79            }
80            currentIterator = null;
81        }
82    }
83
84    @SuppressWarnings("rawtypes")
85    private final static Iterator EMPTY = new Iterator() {
86        public boolean hasNext() {
87            return false;
88        }
89
90        @Override
91        public Object next() {
92            return null;
93        }
94    };
95}
96