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 17 package android.util; 18 19 import java.util.AbstractSet; 20 import 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 */ 30 public final class FastImmutableArraySet<T> extends AbstractSet<T> { 31 FastIterator<T> mIterator; 32 T[] mContents; 33 FastImmutableArraySet(T[] contents)34 public FastImmutableArraySet(T[] contents) { 35 mContents = contents; 36 } 37 38 @Override iterator()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 size()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 FastIterator(T[] contents)59 public FastIterator(T[] contents) { 60 mContents = contents; 61 } 62 63 @Override hasNext()64 public boolean hasNext() { 65 return mIndex != mContents.length; 66 } 67 68 @Override next()69 public T next() { 70 return mContents[mIndex++]; 71 } 72 73 @Override remove()74 public void remove() { 75 throw new UnsupportedOperationException(); 76 } 77 } 78 } 79