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 com.android.internal.util.ArrayUtils;
20 import com.android.internal.util.GrowingArrayUtils;
21 
22 import libcore.util.EmptyArray;
23 
24 /**
25  * SparseLongArrays map integers to longs.  Unlike a normal array of longs,
26  * there can be gaps in the indices.  It is intended to be more memory efficient
27  * than using a HashMap to map Integers to Longs, both because it avoids
28  * auto-boxing keys and values 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>It is possible to iterate over the items in this container using
40  * {@link #keyAt(int)} and {@link #valueAt(int)}. Iterating over the keys using
41  * <code>keyAt(int)</code> with ascending values of the index will return the
42  * keys in ascending order, or the values corresponding to the keys in ascending
43  * order in the case of <code>valueAt(int)</code>.</p>
44  */
45 public class SparseLongArray implements Cloneable {
46     private int[] mKeys;
47     private long[] mValues;
48     private int mSize;
49 
50     /**
51      * Creates a new SparseLongArray containing no mappings.
52      */
SparseLongArray()53     public SparseLongArray() {
54         this(10);
55     }
56 
57     /**
58      * Creates a new SparseLongArray containing no mappings that will not
59      * require any additional memory allocation to store the specified
60      * number of mappings.  If you supply an initial capacity of 0, the
61      * sparse array will be initialized with a light-weight representation
62      * not requiring any additional array allocations.
63      */
SparseLongArray(int initialCapacity)64     public SparseLongArray(int initialCapacity) {
65         if (initialCapacity == 0) {
66             mKeys = EmptyArray.INT;
67             mValues = EmptyArray.LONG;
68         } else {
69             mValues = ArrayUtils.newUnpaddedLongArray(initialCapacity);
70             mKeys = new int[mValues.length];
71         }
72         mSize = 0;
73     }
74 
75     @Override
clone()76     public SparseLongArray clone() {
77         SparseLongArray clone = null;
78         try {
79             clone = (SparseLongArray) super.clone();
80             clone.mKeys = mKeys.clone();
81             clone.mValues = mValues.clone();
82         } catch (CloneNotSupportedException cnse) {
83             /* ignore */
84         }
85         return clone;
86     }
87 
88     /**
89      * Gets the long mapped from the specified key, or <code>0</code>
90      * if no such mapping has been made.
91      */
get(int key)92     public long get(int key) {
93         return get(key, 0);
94     }
95 
96     /**
97      * Gets the long mapped from the specified key, or the specified value
98      * if no such mapping has been made.
99      */
get(int key, long valueIfKeyNotFound)100     public long get(int key, long valueIfKeyNotFound) {
101         int i = ContainerHelpers.binarySearch(mKeys, mSize, key);
102 
103         if (i < 0) {
104             return valueIfKeyNotFound;
105         } else {
106             return mValues[i];
107         }
108     }
109 
110     /**
111      * Removes the mapping from the specified key, if there was any.
112      */
delete(int key)113     public void delete(int key) {
114         int i = ContainerHelpers.binarySearch(mKeys, mSize, key);
115 
116         if (i >= 0) {
117             removeAt(i);
118         }
119     }
120 
121     /**
122      * Removes the mapping at the given index.
123      */
removeAt(int index)124     public void removeAt(int index) {
125         System.arraycopy(mKeys, index + 1, mKeys, index, mSize - (index + 1));
126         System.arraycopy(mValues, index + 1, mValues, index, mSize - (index + 1));
127         mSize--;
128     }
129 
130     /**
131      * Adds a mapping from the specified key to the specified value,
132      * replacing the previous mapping from the specified key if there
133      * was one.
134      */
put(int key, long value)135     public void put(int key, long value) {
136         int i = ContainerHelpers.binarySearch(mKeys, mSize, key);
137 
138         if (i >= 0) {
139             mValues[i] = value;
140         } else {
141             i = ~i;
142 
143             mKeys = GrowingArrayUtils.insert(mKeys, mSize, i, key);
144             mValues = GrowingArrayUtils.insert(mValues, mSize, i, value);
145             mSize++;
146         }
147     }
148 
149     /**
150      * Returns the number of key-value mappings that this SparseIntArray
151      * currently stores.
152      */
size()153     public int size() {
154         return mSize;
155     }
156 
157     /**
158      * Given an index in the range <code>0...size()-1</code>, returns
159      * the key from the <code>index</code>th key-value mapping that this
160      * SparseLongArray stores.
161      *
162      * <p>The keys corresponding to indices in ascending order are guaranteed to
163      * be in ascending order, e.g., <code>keyAt(0)</code> will return the
164      * smallest key and <code>keyAt(size()-1)</code> will return the largest
165      * key.</p>
166      */
keyAt(int index)167     public int keyAt(int index) {
168         return mKeys[index];
169     }
170 
171     /**
172      * Given an index in the range <code>0...size()-1</code>, returns
173      * the value from the <code>index</code>th key-value mapping that this
174      * SparseLongArray stores.
175      *
176      * <p>The values corresponding to indices in ascending order are guaranteed
177      * to be associated with keys in ascending order, e.g.,
178      * <code>valueAt(0)</code> will return the value associated with the
179      * smallest key and <code>valueAt(size()-1)</code> will return the value
180      * associated with the largest key.</p>
181      */
valueAt(int index)182     public long valueAt(int index) {
183         return mValues[index];
184     }
185 
186     /**
187      * Returns the index for which {@link #keyAt} would return the
188      * specified key, or a negative number if the specified
189      * key is not mapped.
190      */
indexOfKey(int key)191     public int indexOfKey(int key) {
192         return ContainerHelpers.binarySearch(mKeys, mSize, key);
193     }
194 
195     /**
196      * Returns an index for which {@link #valueAt} would return the
197      * specified key, or a negative number if no keys map to the
198      * specified value.
199      * Beware that this is a linear search, unlike lookups by key,
200      * and that multiple keys can map to the same value and this will
201      * find only one of them.
202      */
indexOfValue(long value)203     public int indexOfValue(long value) {
204         for (int i = 0; i < mSize; i++)
205             if (mValues[i] == value)
206                 return i;
207 
208         return -1;
209     }
210 
211     /**
212      * Removes all key-value mappings from this SparseIntArray.
213      */
clear()214     public void clear() {
215         mSize = 0;
216     }
217 
218     /**
219      * Puts a key/value pair into the array, optimizing for the case where
220      * the key is greater than all existing keys in the array.
221      */
append(int key, long value)222     public void append(int key, long value) {
223         if (mSize != 0 && key <= mKeys[mSize - 1]) {
224             put(key, value);
225             return;
226         }
227 
228         mKeys = GrowingArrayUtils.append(mKeys, mSize, key);
229         mValues = GrowingArrayUtils.append(mValues, mSize, value);
230         mSize++;
231     }
232 
233     /**
234      * {@inheritDoc}
235      *
236      * <p>This implementation composes a string by iterating over its mappings.
237      */
238     @Override
toString()239     public String toString() {
240         if (size() <= 0) {
241             return "{}";
242         }
243 
244         StringBuilder buffer = new StringBuilder(mSize * 28);
245         buffer.append('{');
246         for (int i=0; i<mSize; i++) {
247             if (i > 0) {
248                 buffer.append(", ");
249             }
250             int key = keyAt(i);
251             buffer.append(key);
252             buffer.append('=');
253             long value = valueAt(i);
254             buffer.append(value);
255         }
256         buffer.append('}');
257         return buffer.toString();
258     }
259 }
260