79 lines
2.2 KiB
Java
79 lines
2.2 KiB
Java
/*
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* Copyright (C) 2011 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package android.util;
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import java.util.AbstractSet;
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import java.util.Iterator;
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/**
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* A fast immutable set wrapper for an array that is optimized for non-concurrent iteration.
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* The same iterator instance is reused each time to avoid creating lots of garbage.
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* Iterating over an array in this fashion is 2.5x faster than iterating over a {@link HashSet}
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* so it is worth copying the contents of the set to an array when iterating over it
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* hundreds of times.
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* @hide
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*/
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public final class FastImmutableArraySet<T> extends AbstractSet<T> {
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FastIterator<T> mIterator;
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T[] mContents;
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public FastImmutableArraySet(T[] contents) {
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mContents = contents;
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}
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@Override
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public Iterator<T> iterator() {
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FastIterator<T> it = mIterator;
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if (it == null) {
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it = new FastIterator<T>(mContents);
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mIterator = it;
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} else {
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it.mIndex = 0;
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}
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return it;
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}
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@Override
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public int size() {
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return mContents.length;
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}
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private static final class FastIterator<T> implements Iterator<T> {
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private final T[] mContents;
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int mIndex;
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public FastIterator(T[] contents) {
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mContents = contents;
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}
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@Override
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public boolean hasNext() {
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return mIndex != mContents.length;
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}
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@Override
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public T next() {
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return mContents[mIndex++];
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}
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@Override
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public void remove() {
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throw new UnsupportedOperationException();
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}
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}
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}
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