1/*
2 * Copyright (C) 2011 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package android.util;
18
19import java.util.AbstractSet;
20import java.util.Iterator;
21
22/**
23 * A fast immutable set wrapper for an array that is optimized for non-concurrent iteration.
24 * The same iterator instance is reused each time to avoid creating lots of garbage.
25 * Iterating over an array in this fashion is 2.5x faster than iterating over a {@link HashSet}
26 * so it is worth copying the contents of the set to an array when iterating over it
27 * hundreds of times.
28 * @hide
29 */
30public final class FastImmutableArraySet<T> extends AbstractSet<T> {
31    FastIterator<T> mIterator;
32    T[] mContents;
33
34    public FastImmutableArraySet(T[] contents) {
35        mContents = contents;
36    }
37
38    @Override
39    public Iterator<T> iterator() {
40        FastIterator<T> it = mIterator;
41        if (it == null) {
42            it = new FastIterator<T>(mContents);
43            mIterator = it;
44        } else {
45            it.mIndex = 0;
46        }
47        return it;
48    }
49
50    @Override
51    public int size() {
52        return mContents.length;
53    }
54
55    private static final class FastIterator<T> implements Iterator<T> {
56        private final T[] mContents;
57        int mIndex;
58
59        public FastIterator(T[] contents) {
60            mContents = contents;
61        }
62
63        @Override
64        public boolean hasNext() {
65            return mIndex != mContents.length;
66        }
67
68        @Override
69        public T next() {
70            return mContents[mIndex++];
71        }
72
73        @Override
74        public void remove() {
75            throw new UnsupportedOperationException();
76        }
77    }
78}
79