1 /*
2  * Copyright (C) 2006 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  * SparseBooleanArrays map integers to booleans.
26  * Unlike a normal array of booleans
27  * there can be gaps in the indices.  It is intended to be more memory efficient
28  * than using a HashMap to map Integers to Booleans, both because it avoids
29  * auto-boxing keys and values and its data structure doesn't rely on an extra entry object
30  * for each mapping.
31  *
32  * <p>Note that this container keeps its mappings in an array data structure,
33  * using a binary search to find keys.  The implementation is not intended to be appropriate for
34  * data structures
35  * that may contain large numbers of items.  It is generally slower than a traditional
36  * HashMap, since lookups require a binary search and adds and removes require inserting
37  * and deleting entries in the array.  For containers holding up to hundreds of items,
38  * the performance difference is not significant, less than 50%.</p>
39  *
40  * <p>It is possible to iterate over the items in this container using
41  * {@link #keyAt(int)} and {@link #valueAt(int)}. Iterating over the keys using
42  * <code>keyAt(int)</code> with ascending values of the index will return the
43  * keys in ascending order, or the values corresponding to the keys in ascending
44  * order in the case of <code>valueAt(int)</code>.</p>
45  */
46 public class SparseBooleanArray implements Cloneable {
47     /**
48      * Creates a new SparseBooleanArray containing no mappings.
49      */
SparseBooleanArray()50     public SparseBooleanArray() {
51         this(10);
52     }
53 
54     /**
55      * Creates a new SparseBooleanArray containing no mappings that will not
56      * require any additional memory allocation to store the specified
57      * number of mappings.  If you supply an initial capacity of 0, the
58      * sparse array will be initialized with a light-weight representation
59      * not requiring any additional array allocations.
60      */
SparseBooleanArray(int initialCapacity)61     public SparseBooleanArray(int initialCapacity) {
62         if (initialCapacity == 0) {
63             mKeys = EmptyArray.INT;
64             mValues = EmptyArray.BOOLEAN;
65         } else {
66             mKeys = ArrayUtils.newUnpaddedIntArray(initialCapacity);
67             mValues = new boolean[mKeys.length];
68         }
69         mSize = 0;
70     }
71 
72     @Override
clone()73     public SparseBooleanArray clone() {
74         SparseBooleanArray clone = null;
75         try {
76             clone = (SparseBooleanArray) super.clone();
77             clone.mKeys = mKeys.clone();
78             clone.mValues = mValues.clone();
79         } catch (CloneNotSupportedException cnse) {
80             /* ignore */
81         }
82         return clone;
83     }
84 
85     /**
86      * Gets the boolean mapped from the specified key, or <code>false</code>
87      * if no such mapping has been made.
88      */
get(int key)89     public boolean get(int key) {
90         return get(key, false);
91     }
92 
93     /**
94      * Gets the boolean mapped from the specified key, or the specified value
95      * if no such mapping has been made.
96      */
get(int key, boolean valueIfKeyNotFound)97     public boolean get(int key, boolean valueIfKeyNotFound) {
98         int i = ContainerHelpers.binarySearch(mKeys, mSize, key);
99 
100         if (i < 0) {
101             return valueIfKeyNotFound;
102         } else {
103             return mValues[i];
104         }
105     }
106 
107     /**
108      * Removes the mapping from the specified key, if there was any.
109      */
delete(int key)110     public void delete(int key) {
111         int i = ContainerHelpers.binarySearch(mKeys, mSize, key);
112 
113         if (i >= 0) {
114             System.arraycopy(mKeys, i + 1, mKeys, i, mSize - (i + 1));
115             System.arraycopy(mValues, i + 1, mValues, i, mSize - (i + 1));
116             mSize--;
117         }
118     }
119 
120     /** @hide */
removeAt(int index)121     public void removeAt(int index) {
122         System.arraycopy(mKeys, index + 1, mKeys, index, mSize - (index + 1));
123         System.arraycopy(mValues, index + 1, mValues, index, mSize - (index + 1));
124         mSize--;
125     }
126 
127     /**
128      * Adds a mapping from the specified key to the specified value,
129      * replacing the previous mapping from the specified key if there
130      * was one.
131      */
put(int key, boolean value)132     public void put(int key, boolean value) {
133         int i = ContainerHelpers.binarySearch(mKeys, mSize, key);
134 
135         if (i >= 0) {
136             mValues[i] = value;
137         } else {
138             i = ~i;
139 
140             mKeys = GrowingArrayUtils.insert(mKeys, mSize, i, key);
141             mValues = GrowingArrayUtils.insert(mValues, mSize, i, value);
142             mSize++;
143         }
144     }
145 
146     /**
147      * Returns the number of key-value mappings that this SparseBooleanArray
148      * currently stores.
149      */
size()150     public int size() {
151         return mSize;
152     }
153 
154     /**
155      * Given an index in the range <code>0...size()-1</code>, returns
156      * the key from the <code>index</code>th key-value mapping that this
157      * SparseBooleanArray stores.
158      *
159      * <p>The keys corresponding to indices in ascending order are guaranteed to
160      * be in ascending order, e.g., <code>keyAt(0)</code> will return the
161      * smallest key and <code>keyAt(size()-1)</code> will return the largest
162      * key.</p>
163      */
keyAt(int index)164     public int keyAt(int index) {
165         return mKeys[index];
166     }
167 
168     /**
169      * Given an index in the range <code>0...size()-1</code>, returns
170      * the value from the <code>index</code>th key-value mapping that this
171      * SparseBooleanArray stores.
172      *
173      * <p>The values corresponding to indices in ascending order are guaranteed
174      * to be associated with keys in ascending order, e.g.,
175      * <code>valueAt(0)</code> will return the value associated with the
176      * smallest key and <code>valueAt(size()-1)</code> will return the value
177      * associated with the largest key.</p>
178      */
valueAt(int index)179     public boolean valueAt(int index) {
180         return mValues[index];
181     }
182 
183     /** @hide */
setValueAt(int index, boolean value)184     public void setValueAt(int index, boolean value) {
185         mValues[index] = value;
186     }
187 
188     /**
189      * Returns the index for which {@link #keyAt} would return the
190      * specified key, or a negative number if the specified
191      * key is not mapped.
192      */
indexOfKey(int key)193     public int indexOfKey(int key) {
194         return ContainerHelpers.binarySearch(mKeys, mSize, key);
195     }
196 
197     /**
198      * Returns an index for which {@link #valueAt} would return the
199      * specified key, or a negative number if no keys map to the
200      * specified value.
201      * Beware that this is a linear search, unlike lookups by key,
202      * and that multiple keys can map to the same value and this will
203      * find only one of them.
204      */
indexOfValue(boolean value)205     public int indexOfValue(boolean value) {
206         for (int i = 0; i < mSize; i++)
207             if (mValues[i] == value)
208                 return i;
209 
210         return -1;
211     }
212 
213     /**
214      * Removes all key-value mappings from this SparseBooleanArray.
215      */
clear()216     public void clear() {
217         mSize = 0;
218     }
219 
220     /**
221      * Puts a key/value pair into the array, optimizing for the case where
222      * the key is greater than all existing keys in the array.
223      */
append(int key, boolean value)224     public void append(int key, boolean value) {
225         if (mSize != 0 && key <= mKeys[mSize - 1]) {
226             put(key, value);
227             return;
228         }
229 
230         mKeys = GrowingArrayUtils.append(mKeys, mSize, key);
231         mValues = GrowingArrayUtils.append(mValues, mSize, value);
232         mSize++;
233     }
234 
235     /**
236      * {@inheritDoc}
237      *
238      * <p>This implementation composes a string by iterating over its mappings.
239      */
240     @Override
toString()241     public String toString() {
242         if (size() <= 0) {
243             return "{}";
244         }
245 
246         StringBuilder buffer = new StringBuilder(mSize * 28);
247         buffer.append('{');
248         for (int i=0; i<mSize; i++) {
249             if (i > 0) {
250                 buffer.append(", ");
251             }
252             int key = keyAt(i);
253             buffer.append(key);
254             buffer.append('=');
255             boolean value = valueAt(i);
256             buffer.append(value);
257         }
258         buffer.append('}');
259         return buffer.toString();
260     }
261 
262     private int[] mKeys;
263     private boolean[] mValues;
264     private int mSize;
265 }
266