1 /*
2  * Copyright (C) 2009 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 com.android.internal.util.ArrayUtils;
20 import com.android.internal.util.GrowingArrayUtils;
21 
22 import libcore.util.EmptyArray;
23 
24 /**
25  * SparseArray mapping longs to Objects.  Unlike a normal array of Objects,
26  * there can be gaps in the indices.  It is intended to be more memory efficient
27  * than using a HashMap to map Longs to Objects, both because it avoids
28  * auto-boxing keys and its data structure doesn't rely on an extra entry object
29  * for each mapping.
30  *
31  * <p>Note that this container keeps its mappings in an array data structure,
32  * using a binary search to find keys.  The implementation is not intended to be appropriate for
33  * data structures
34  * that may contain large numbers of items.  It is generally slower than a traditional
35  * HashMap, since lookups require a binary search and adds and removes require inserting
36  * and deleting entries in the array.  For containers holding up to hundreds of items,
37  * the performance difference is not significant, less than 50%.</p>
38  *
39  * <p>To help with performance, the container includes an optimization when removing
40  * keys: instead of compacting its array immediately, it leaves the removed entry marked
41  * as deleted.  The entry can then be re-used for the same key, or compacted later in
42  * a single garbage collection step of all removed entries.  This garbage collection will
43  * need to be performed at any time the array needs to be grown or the the map size or
44  * entry values are retrieved.</p>
45  *
46  * <p>It is possible to iterate over the items in this container using
47  * {@link #keyAt(int)} and {@link #valueAt(int)}. Iterating over the keys using
48  * <code>keyAt(int)</code> with ascending values of the index will return the
49  * keys in ascending order, or the values corresponding to the keys in ascending
50  * order in the case of <code>valueAt(int)</code>.</p>
51  */
52 public class LongSparseArray<E> implements Cloneable {
53     private static final Object DELETED = new Object();
54     private boolean mGarbage = false;
55 
56     private long[] mKeys;
57     private Object[] mValues;
58     private int mSize;
59 
60     /**
61      * Creates a new LongSparseArray containing no mappings.
62      */
LongSparseArray()63     public LongSparseArray() {
64         this(10);
65     }
66 
67     /**
68      * Creates a new LongSparseArray containing no mappings that will not
69      * require any additional memory allocation to store the specified
70      * number of mappings.  If you supply an initial capacity of 0, the
71      * sparse array will be initialized with a light-weight representation
72      * not requiring any additional array allocations.
73      */
LongSparseArray(int initialCapacity)74     public LongSparseArray(int initialCapacity) {
75         if (initialCapacity == 0) {
76             mKeys = EmptyArray.LONG;
77             mValues = EmptyArray.OBJECT;
78         } else {
79             mKeys = ArrayUtils.newUnpaddedLongArray(initialCapacity);
80             mValues = ArrayUtils.newUnpaddedObjectArray(initialCapacity);
81         }
82         mSize = 0;
83     }
84 
85     @Override
86     @SuppressWarnings("unchecked")
clone()87     public LongSparseArray<E> clone() {
88         LongSparseArray<E> clone = null;
89         try {
90             clone = (LongSparseArray<E>) super.clone();
91             clone.mKeys = mKeys.clone();
92             clone.mValues = mValues.clone();
93         } catch (CloneNotSupportedException cnse) {
94             /* ignore */
95         }
96         return clone;
97     }
98 
99     /**
100      * Gets the Object mapped from the specified key, or <code>null</code>
101      * if no such mapping has been made.
102      */
get(long key)103     public E get(long key) {
104         return get(key, null);
105     }
106 
107     /**
108      * Gets the Object mapped from the specified key, or the specified Object
109      * if no such mapping has been made.
110      */
111     @SuppressWarnings("unchecked")
get(long key, E valueIfKeyNotFound)112     public E get(long key, E valueIfKeyNotFound) {
113         int i = ContainerHelpers.binarySearch(mKeys, mSize, key);
114 
115         if (i < 0 || mValues[i] == DELETED) {
116             return valueIfKeyNotFound;
117         } else {
118             return (E) mValues[i];
119         }
120     }
121 
122     /**
123      * Removes the mapping from the specified key, if there was any.
124      */
delete(long key)125     public void delete(long key) {
126         int i = ContainerHelpers.binarySearch(mKeys, mSize, key);
127 
128         if (i >= 0) {
129             if (mValues[i] != DELETED) {
130                 mValues[i] = DELETED;
131                 mGarbage = true;
132             }
133         }
134     }
135 
136     /**
137      * Alias for {@link #delete(long)}.
138      */
remove(long key)139     public void remove(long key) {
140         delete(key);
141     }
142 
143     /**
144      * Removes the mapping at the specified index.
145      *
146      * <p>For indices outside of the range <code>0...size()-1</code>, the behavior is undefined for
147      * apps targeting {@link android.os.Build.VERSION_CODES#P} and earlier, and an
148      * {@link ArrayIndexOutOfBoundsException} is thrown for apps targeting
149      * {@link android.os.Build.VERSION_CODES#Q} and later.</p>
150      */
removeAt(int index)151     public void removeAt(int index) {
152         if (index >= mSize && UtilConfig.sThrowExceptionForUpperArrayOutOfBounds) {
153             // The array might be slightly bigger than mSize, in which case, indexing won't fail.
154             // Check if exception should be thrown outside of the critical path.
155             throw new ArrayIndexOutOfBoundsException(index);
156         }
157         if (mValues[index] != DELETED) {
158             mValues[index] = DELETED;
159             mGarbage = true;
160         }
161     }
162 
gc()163     private void gc() {
164         // Log.e("SparseArray", "gc start with " + mSize);
165 
166         int n = mSize;
167         int o = 0;
168         long[] keys = mKeys;
169         Object[] values = mValues;
170 
171         for (int i = 0; i < n; i++) {
172             Object val = values[i];
173 
174             if (val != DELETED) {
175                 if (i != o) {
176                     keys[o] = keys[i];
177                     values[o] = val;
178                     values[i] = null;
179                 }
180 
181                 o++;
182             }
183         }
184 
185         mGarbage = false;
186         mSize = o;
187 
188         // Log.e("SparseArray", "gc end with " + mSize);
189     }
190 
191     /**
192      * Adds a mapping from the specified key to the specified value,
193      * replacing the previous mapping from the specified key if there
194      * was one.
195      */
put(long key, E value)196     public void put(long key, E value) {
197         int i = ContainerHelpers.binarySearch(mKeys, mSize, key);
198 
199         if (i >= 0) {
200             mValues[i] = value;
201         } else {
202             i = ~i;
203 
204             if (i < mSize && mValues[i] == DELETED) {
205                 mKeys[i] = key;
206                 mValues[i] = value;
207                 return;
208             }
209 
210             if (mGarbage && mSize >= mKeys.length) {
211                 gc();
212 
213                 // Search again because indices may have changed.
214                 i = ~ContainerHelpers.binarySearch(mKeys, mSize, key);
215             }
216 
217             mKeys = GrowingArrayUtils.insert(mKeys, mSize, i, key);
218             mValues = GrowingArrayUtils.insert(mValues, mSize, i, value);
219             mSize++;
220         }
221     }
222 
223     /**
224      * Returns the number of key-value mappings that this LongSparseArray
225      * currently stores.
226      */
size()227     public int size() {
228         if (mGarbage) {
229             gc();
230         }
231 
232         return mSize;
233     }
234 
235     /**
236      * Given an index in the range <code>0...size()-1</code>, returns
237      * the key from the <code>index</code>th key-value mapping that this
238      * LongSparseArray stores.
239      *
240      * <p>The keys corresponding to indices in ascending order are guaranteed to
241      * be in ascending order, e.g., <code>keyAt(0)</code> will return the
242      * smallest key and <code>keyAt(size()-1)</code> will return the largest
243      * key.</p>
244      *
245      * <p>For indices outside of the range <code>0...size()-1</code>, the behavior is undefined for
246      * apps targeting {@link android.os.Build.VERSION_CODES#P} and earlier, and an
247      * {@link ArrayIndexOutOfBoundsException} is thrown for apps targeting
248      * {@link android.os.Build.VERSION_CODES#Q} and later.</p>
249      */
keyAt(int index)250     public long keyAt(int index) {
251         if (index >= mSize && UtilConfig.sThrowExceptionForUpperArrayOutOfBounds) {
252             // The array might be slightly bigger than mSize, in which case, indexing won't fail.
253             // Check if exception should be thrown outside of the critical path.
254             throw new ArrayIndexOutOfBoundsException(index);
255         }
256         if (mGarbage) {
257             gc();
258         }
259 
260         return mKeys[index];
261     }
262 
263     /**
264      * Given an index in the range <code>0...size()-1</code>, returns
265      * the value from the <code>index</code>th key-value mapping that this
266      * LongSparseArray stores.
267      *
268      * <p>The values corresponding to indices in ascending order are guaranteed
269      * to be associated with keys in ascending order, e.g.,
270      * <code>valueAt(0)</code> will return the value associated with the
271      * smallest key and <code>valueAt(size()-1)</code> will return the value
272      * associated with the largest key.</p>
273      *
274      * <p>For indices outside of the range <code>0...size()-1</code>, the behavior is undefined for
275      * apps targeting {@link android.os.Build.VERSION_CODES#P} and earlier, and an
276      * {@link ArrayIndexOutOfBoundsException} is thrown for apps targeting
277      * {@link android.os.Build.VERSION_CODES#Q} and later.</p>
278      */
279     @SuppressWarnings("unchecked")
valueAt(int index)280     public E valueAt(int index) {
281         if (index >= mSize && UtilConfig.sThrowExceptionForUpperArrayOutOfBounds) {
282             // The array might be slightly bigger than mSize, in which case, indexing won't fail.
283             // Check if exception should be thrown outside of the critical path.
284             throw new ArrayIndexOutOfBoundsException(index);
285         }
286         if (mGarbage) {
287             gc();
288         }
289 
290         return (E) mValues[index];
291     }
292 
293     /**
294      * Given an index in the range <code>0...size()-1</code>, sets a new
295      * value for the <code>index</code>th key-value mapping that this
296      * LongSparseArray stores.
297      *
298      * <p>For indices outside of the range <code>0...size()-1</code>, the behavior is undefined for
299      * apps targeting {@link android.os.Build.VERSION_CODES#P} and earlier, and an
300      * {@link ArrayIndexOutOfBoundsException} is thrown for apps targeting
301      * {@link android.os.Build.VERSION_CODES#Q} and later.</p>
302      */
setValueAt(int index, E value)303     public void setValueAt(int index, E value) {
304         if (index >= mSize && UtilConfig.sThrowExceptionForUpperArrayOutOfBounds) {
305             // The array might be slightly bigger than mSize, in which case, indexing won't fail.
306             // Check if exception should be thrown outside of the critical path.
307             throw new ArrayIndexOutOfBoundsException(index);
308         }
309         if (mGarbage) {
310             gc();
311         }
312 
313         mValues[index] = value;
314     }
315 
316     /**
317      * Returns the index for which {@link #keyAt} would return the
318      * specified key, or a negative number if the specified
319      * key is not mapped.
320      */
indexOfKey(long key)321     public int indexOfKey(long key) {
322         if (mGarbage) {
323             gc();
324         }
325 
326         return ContainerHelpers.binarySearch(mKeys, mSize, key);
327     }
328 
329     /**
330      * Returns an index for which {@link #valueAt} would return the
331      * specified key, or a negative number if no keys map to the
332      * specified value.
333      * Beware that this is a linear search, unlike lookups by key,
334      * and that multiple keys can map to the same value and this will
335      * find only one of them.
336      */
indexOfValue(E value)337     public int indexOfValue(E value) {
338         if (mGarbage) {
339             gc();
340         }
341 
342         for (int i = 0; i < mSize; i++) {
343             if (mValues[i] == value) {
344                 return i;
345             }
346         }
347         return -1;
348     }
349 
350     /**
351      * Returns an index for which {@link #valueAt} would return the
352      * specified key, or a negative number if no keys map to the
353      * specified value.
354      * <p>Beware that this is a linear search, unlike lookups by key,
355      * and that multiple keys can map to the same value and this will
356      * find only one of them.
357      * <p>Note also that this method uses {@code equals} unlike {@code indexOfValue}.
358      * @hide
359      */
indexOfValueByValue(E value)360     public int indexOfValueByValue(E value) {
361         if (mGarbage) {
362             gc();
363         }
364 
365         for (int i = 0; i < mSize; i++) {
366             if (value == null) {
367                 if (mValues[i] == null) {
368                     return i;
369                 }
370             } else {
371                 if (value.equals(mValues[i])) {
372                     return i;
373                 }
374             }
375         }
376         return -1;
377     }
378 
379     /**
380      * Removes all key-value mappings from this LongSparseArray.
381      */
clear()382     public void clear() {
383         int n = mSize;
384         Object[] values = mValues;
385 
386         for (int i = 0; i < n; i++) {
387             values[i] = null;
388         }
389 
390         mSize = 0;
391         mGarbage = false;
392     }
393 
394     /**
395      * Puts a key/value pair into the array, optimizing for the case where
396      * the key is greater than all existing keys in the array.
397      */
append(long key, E value)398     public void append(long key, E value) {
399         if (mSize != 0 && key <= mKeys[mSize - 1]) {
400             put(key, value);
401             return;
402         }
403 
404         if (mGarbage && mSize >= mKeys.length) {
405             gc();
406         }
407 
408         mKeys = GrowingArrayUtils.append(mKeys, mSize, key);
409         mValues = GrowingArrayUtils.append(mValues, mSize, value);
410         mSize++;
411     }
412 
413     /**
414      * {@inheritDoc}
415      *
416      * <p>This implementation composes a string by iterating over its mappings. If
417      * this map contains itself as a value, the string "(this Map)"
418      * will appear in its place.
419      */
420     @Override
toString()421     public String toString() {
422         if (size() <= 0) {
423             return "{}";
424         }
425 
426         StringBuilder buffer = new StringBuilder(mSize * 28);
427         buffer.append('{');
428         for (int i=0; i<mSize; i++) {
429             if (i > 0) {
430                 buffer.append(", ");
431             }
432             long key = keyAt(i);
433             buffer.append(key);
434             buffer.append('=');
435             Object value = valueAt(i);
436             if (value != this) {
437                 buffer.append(value);
438             } else {
439                 buffer.append("(this Map)");
440             }
441         }
442         buffer.append('}');
443         return buffer.toString();
444     }
445 }
446