SparseLongArray.java revision ebb47950f21d3c41955a591000dfb1f195e746fe
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 17package android.util; 18 19import com.android.internal.util.ArrayUtils; 20 21/** 22 * SparseLongArrays map integers to longs. Unlike a normal array of longs, 23 * there can be gaps in the indices. It is intended to be more memory efficient 24 * than using a HashMap to map Integers to Longs, both because it avoids 25 * auto-boxing keys and values and its data structure doesn't rely on an extra entry object 26 * for each mapping. 27 * 28 * <p>Note that this container keeps its mappings in an array data structure, 29 * using a binary search to find keys. The implementation is not intended to be appropriate for 30 * data structures 31 * that may contain large numbers of items. It is generally slower than a traditional 32 * HashMap, since lookups require a binary search and adds and removes require inserting 33 * and deleting entries in the array. For containers holding up to hundreds of items, 34 * the performance difference is not significant, less than 50%.</p> 35 * 36 * <p>It is possible to iterate over the items in this container using 37 * {@link #keyAt(int)} and {@link #valueAt(int)}. Iterating over the keys using 38 * <code>keyAt(int)</code> with ascending values of the index will return the 39 * keys in ascending order, or the values corresponding to the keys in ascending 40 * order in the case of <code>valueAt(int)</code>.</p> 41 */ 42public class SparseLongArray implements Cloneable { 43 private int[] mKeys; 44 private long[] mValues; 45 private int mSize; 46 47 /** 48 * Creates a new SparseLongArray containing no mappings. 49 */ 50 public SparseLongArray() { 51 this(10); 52 } 53 54 /** 55 * Creates a new SparseLongArray 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 */ 61 public SparseLongArray(int initialCapacity) { 62 if (initialCapacity == 0) { 63 mKeys = ContainerHelpers.EMPTY_INTS; 64 mValues = ContainerHelpers.EMPTY_LONGS; 65 } else { 66 initialCapacity = ArrayUtils.idealLongArraySize(initialCapacity); 67 mKeys = new int[initialCapacity]; 68 mValues = new long[initialCapacity]; 69 } 70 mSize = 0; 71 } 72 73 @Override 74 public SparseLongArray clone() { 75 SparseLongArray clone = null; 76 try { 77 clone = (SparseLongArray) super.clone(); 78 clone.mKeys = mKeys.clone(); 79 clone.mValues = mValues.clone(); 80 } catch (CloneNotSupportedException cnse) { 81 /* ignore */ 82 } 83 return clone; 84 } 85 86 /** 87 * Gets the long mapped from the specified key, or <code>0</code> 88 * if no such mapping has been made. 89 */ 90 public long get(int key) { 91 return get(key, 0); 92 } 93 94 /** 95 * Gets the long mapped from the specified key, or the specified value 96 * if no such mapping has been made. 97 */ 98 public long get(int key, long valueIfKeyNotFound) { 99 int i = ContainerHelpers.binarySearch(mKeys, mSize, key); 100 101 if (i < 0) { 102 return valueIfKeyNotFound; 103 } else { 104 return mValues[i]; 105 } 106 } 107 108 /** 109 * Removes the mapping from the specified key, if there was any. 110 */ 111 public void delete(int key) { 112 int i = ContainerHelpers.binarySearch(mKeys, mSize, key); 113 114 if (i >= 0) { 115 removeAt(i); 116 } 117 } 118 119 /** 120 * Removes the mapping at the given index. 121 */ 122 public void removeAt(int index) { 123 System.arraycopy(mKeys, index + 1, mKeys, index, mSize - (index + 1)); 124 System.arraycopy(mValues, index + 1, mValues, index, mSize - (index + 1)); 125 mSize--; 126 } 127 128 /** 129 * Adds a mapping from the specified key to the specified value, 130 * replacing the previous mapping from the specified key if there 131 * was one. 132 */ 133 public void put(int key, long value) { 134 int i = ContainerHelpers.binarySearch(mKeys, mSize, key); 135 136 if (i >= 0) { 137 mValues[i] = value; 138 } else { 139 i = ~i; 140 141 if (mSize >= mKeys.length) { 142 growKeyAndValueArrays(mSize + 1); 143 } 144 145 if (mSize - i != 0) { 146 System.arraycopy(mKeys, i, mKeys, i + 1, mSize - i); 147 System.arraycopy(mValues, i, mValues, i + 1, mSize - i); 148 } 149 150 mKeys[i] = key; 151 mValues[i] = value; 152 mSize++; 153 } 154 } 155 156 /** 157 * Returns the number of key-value mappings that this SparseIntArray 158 * currently stores. 159 */ 160 public int size() { 161 return mSize; 162 } 163 164 /** 165 * Given an index in the range <code>0...size()-1</code>, returns 166 * the key from the <code>index</code>th key-value mapping that this 167 * SparseLongArray stores. 168 * 169 * <p>The keys corresponding to indices in ascending order are guaranteed to 170 * be in ascending order, e.g., <code>keyAt(0)</code> will return the 171 * smallest key and <code>keyAt(size()-1)</code> will return the largest 172 * key.</p> 173 */ 174 public int keyAt(int index) { 175 return mKeys[index]; 176 } 177 178 /** 179 * Given an index in the range <code>0...size()-1</code>, returns 180 * the value from the <code>index</code>th key-value mapping that this 181 * SparseLongArray stores. 182 * 183 * <p>The values corresponding to indices in ascending order are guaranteed 184 * to be associated with keys in ascending order, e.g., 185 * <code>valueAt(0)</code> will return the value associated with the 186 * smallest key and <code>valueAt(size()-1)</code> will return the value 187 * associated with the largest key.</p> 188 */ 189 public long valueAt(int index) { 190 return mValues[index]; 191 } 192 193 /** 194 * Returns the index for which {@link #keyAt} would return the 195 * specified key, or a negative number if the specified 196 * key is not mapped. 197 */ 198 public int indexOfKey(int key) { 199 return ContainerHelpers.binarySearch(mKeys, mSize, key); 200 } 201 202 /** 203 * Returns an index for which {@link #valueAt} would return the 204 * specified key, or a negative number if no keys map to the 205 * specified value. 206 * Beware that this is a linear search, unlike lookups by key, 207 * and that multiple keys can map to the same value and this will 208 * find only one of them. 209 */ 210 public int indexOfValue(long value) { 211 for (int i = 0; i < mSize; i++) 212 if (mValues[i] == value) 213 return i; 214 215 return -1; 216 } 217 218 /** 219 * Removes all key-value mappings from this SparseIntArray. 220 */ 221 public void clear() { 222 mSize = 0; 223 } 224 225 /** 226 * Puts a key/value pair into the array, optimizing for the case where 227 * the key is greater than all existing keys in the array. 228 */ 229 public void append(int key, long value) { 230 if (mSize != 0 && key <= mKeys[mSize - 1]) { 231 put(key, value); 232 return; 233 } 234 235 int pos = mSize; 236 if (pos >= mKeys.length) { 237 growKeyAndValueArrays(pos + 1); 238 } 239 240 mKeys[pos] = key; 241 mValues[pos] = value; 242 mSize = pos + 1; 243 } 244 245 private void growKeyAndValueArrays(int minNeededSize) { 246 int n = ArrayUtils.idealLongArraySize(minNeededSize); 247 248 int[] nkeys = new int[n]; 249 long[] nvalues = new long[n]; 250 251 System.arraycopy(mKeys, 0, nkeys, 0, mKeys.length); 252 System.arraycopy(mValues, 0, nvalues, 0, mValues.length); 253 254 mKeys = nkeys; 255 mValues = nvalues; 256 } 257 258 /** 259 * {@inheritDoc} 260 * 261 * <p>This implementation composes a string by iterating over its mappings. 262 */ 263 @Override 264 public String toString() { 265 if (size() <= 0) { 266 return "{}"; 267 } 268 269 StringBuilder buffer = new StringBuilder(mSize * 28); 270 buffer.append('{'); 271 for (int i=0; i<mSize; i++) { 272 if (i > 0) { 273 buffer.append(", "); 274 } 275 int key = keyAt(i); 276 buffer.append(key); 277 buffer.append('='); 278 long value = valueAt(i); 279 buffer.append(value); 280 } 281 buffer.append('}'); 282 return buffer.toString(); 283 } 284} 285