1 files changed, 78 insertions, 0 deletions
diff --git a/core/java/android/util/FastImmutableArraySet.java b/core/java/android/util/FastImmutableArraySet.java
new file mode 100644
index 000000000000..4175c6057ecf
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+++ b/core/java/android/util/FastImmutableArraySet.java
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+/*
+ * Copyright (C) 2011 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.util;
+
+import java.util.AbstractSet;
+import java.util.Iterator;
+
+/**
+ * A fast immutable set wrapper for an array that is optimized for non-concurrent iteration.
+ * The same iterator instance is reused each time to avoid creating lots of garbage.
+ * Iterating over an array in this fashion is 2.5x faster than iterating over a {@link HashSet}
+ * so it is worth copying the contents of the set to an array when iterating over it
+ * hundreds of times.
+ * @hide
+ */
+public final class FastImmutableArraySet<T> extends AbstractSet<T> {
+    FastIterator<T> mIterator;
+    T[] mContents;
+
+    public FastImmutableArraySet(T[] contents) {
+        mContents = contents;
+    }
+
+    @Override
+    public Iterator<T> iterator() {
+        FastIterator<T> it = mIterator;
+        if (it == null) {
+            it = new FastIterator<T>(mContents);
+            mIterator = it;
+        } else {
+            it.mIndex = 0;
+        }
+        return it;
+    }
+
+    @Override
+    public int size() {
+        return mContents.length;
+    }
+
+    private static final class FastIterator<T> implements Iterator<T> {
+        private final T[] mContents;
+        int mIndex;
+
+        public FastIterator(T[] contents) {
+            mContents = contents;
+        }
+
+        @Override
+        public boolean hasNext() {
+            return mIndex != mContents.length;
+        }
+
+        @Override
+        public T next() {
+            return mContents[mIndex++];
+        }
+
+        @Override
+        public void remove() {
+            throw new UnsupportedOperationException();
+        }
+    }
+}