SparseLongArray.java revision 3e82ba1a67b0c756ab6a289985f4cfc53725b311
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 */ 36public class SparseLongArray implements Cloneable { 37 private int[] mKeys; 38 private long[] mValues; 39 private int mSize; 40 41 /** 42 * Creates a new SparseLongArray containing no mappings. 43 */ 44 public SparseLongArray() { 45 this(10); 46 } 47 48 /** 49 * Creates a new SparseLongArray containing no mappings that will not 50 * require any additional memory allocation to store the specified 51 * number of mappings. If you supply an initial capacity of 0, the 52 * sparse array will be initialized with a light-weight representation 53 * not requiring any additional array allocations. 54 */ 55 public SparseLongArray(int initialCapacity) { 56 if (initialCapacity == 0) { 57 mKeys = ContainerHelpers.EMPTY_INTS; 58 mValues = ContainerHelpers.EMPTY_LONGS; 59 } else { 60 initialCapacity = ArrayUtils.idealLongArraySize(initialCapacity); 61 mKeys = new int[initialCapacity]; 62 mValues = new long[initialCapacity]; 63 } 64 mSize = 0; 65 } 66 67 @Override 68 public SparseLongArray clone() { 69 SparseLongArray clone = null; 70 try { 71 clone = (SparseLongArray) super.clone(); 72 clone.mKeys = mKeys.clone(); 73 clone.mValues = mValues.clone(); 74 } catch (CloneNotSupportedException cnse) { 75 /* ignore */ 76 } 77 return clone; 78 } 79 80 /** 81 * Gets the long mapped from the specified key, or <code>0</code> 82 * if no such mapping has been made. 83 */ 84 public long get(int key) { 85 return get(key, 0); 86 } 87 88 /** 89 * Gets the long mapped from the specified key, or the specified value 90 * if no such mapping has been made. 91 */ 92 public long get(int key, long valueIfKeyNotFound) { 93 int i = ContainerHelpers.binarySearch(mKeys, mSize, key); 94 95 if (i < 0) { 96 return valueIfKeyNotFound; 97 } else { 98 return mValues[i]; 99 } 100 } 101 102 /** 103 * Removes the mapping from the specified key, if there was any. 104 */ 105 public void delete(int key) { 106 int i = ContainerHelpers.binarySearch(mKeys, mSize, key); 107 108 if (i >= 0) { 109 removeAt(i); 110 } 111 } 112 113 /** 114 * Removes the mapping at the given index. 115 */ 116 public void removeAt(int index) { 117 System.arraycopy(mKeys, index + 1, mKeys, index, mSize - (index + 1)); 118 System.arraycopy(mValues, index + 1, mValues, index, mSize - (index + 1)); 119 mSize--; 120 } 121 122 /** 123 * Adds a mapping from the specified key to the specified value, 124 * replacing the previous mapping from the specified key if there 125 * was one. 126 */ 127 public void put(int key, long value) { 128 int i = ContainerHelpers.binarySearch(mKeys, mSize, key); 129 130 if (i >= 0) { 131 mValues[i] = value; 132 } else { 133 i = ~i; 134 135 if (mSize >= mKeys.length) { 136 growKeyAndValueArrays(mSize + 1); 137 } 138 139 if (mSize - i != 0) { 140 System.arraycopy(mKeys, i, mKeys, i + 1, mSize - i); 141 System.arraycopy(mValues, i, mValues, i + 1, mSize - i); 142 } 143 144 mKeys[i] = key; 145 mValues[i] = value; 146 mSize++; 147 } 148 } 149 150 /** 151 * Returns the number of key-value mappings that this SparseIntArray 152 * currently stores. 153 */ 154 public int size() { 155 return mSize; 156 } 157 158 /** 159 * Given an index in the range <code>0...size()-1</code>, returns 160 * the key from the <code>index</code>th key-value mapping that this 161 * SparseLongArray stores. 162 */ 163 public int keyAt(int index) { 164 return mKeys[index]; 165 } 166 167 /** 168 * Given an index in the range <code>0...size()-1</code>, returns 169 * the value from the <code>index</code>th key-value mapping that this 170 * SparseLongArray stores. 171 */ 172 public long valueAt(int index) { 173 return mValues[index]; 174 } 175 176 /** 177 * Returns the index for which {@link #keyAt} would return the 178 * specified key, or a negative number if the specified 179 * key is not mapped. 180 */ 181 public int indexOfKey(int key) { 182 return ContainerHelpers.binarySearch(mKeys, mSize, key); 183 } 184 185 /** 186 * Returns an index for which {@link #valueAt} would return the 187 * specified key, or a negative number if no keys map to the 188 * specified value. 189 * Beware that this is a linear search, unlike lookups by key, 190 * and that multiple keys can map to the same value and this will 191 * find only one of them. 192 */ 193 public int indexOfValue(long value) { 194 for (int i = 0; i < mSize; i++) 195 if (mValues[i] == value) 196 return i; 197 198 return -1; 199 } 200 201 /** 202 * Removes all key-value mappings from this SparseIntArray. 203 */ 204 public void clear() { 205 mSize = 0; 206 } 207 208 /** 209 * Puts a key/value pair into the array, optimizing for the case where 210 * the key is greater than all existing keys in the array. 211 */ 212 public void append(int key, long value) { 213 if (mSize != 0 && key <= mKeys[mSize - 1]) { 214 put(key, value); 215 return; 216 } 217 218 int pos = mSize; 219 if (pos >= mKeys.length) { 220 growKeyAndValueArrays(pos + 1); 221 } 222 223 mKeys[pos] = key; 224 mValues[pos] = value; 225 mSize = pos + 1; 226 } 227 228 private void growKeyAndValueArrays(int minNeededSize) { 229 int n = ArrayUtils.idealLongArraySize(minNeededSize); 230 231 int[] nkeys = new int[n]; 232 long[] nvalues = new long[n]; 233 234 System.arraycopy(mKeys, 0, nkeys, 0, mKeys.length); 235 System.arraycopy(mValues, 0, nvalues, 0, mValues.length); 236 237 mKeys = nkeys; 238 mValues = nvalues; 239 } 240 241 /** 242 * {@inheritDoc} 243 * 244 * <p>This implementation composes a string by iterating over its mappings. 245 */ 246 @Override 247 public String toString() { 248 if (size() <= 0) { 249 return "{}"; 250 } 251 252 StringBuilder buffer = new StringBuilder(mSize * 28); 253 buffer.append('{'); 254 for (int i=0; i<mSize; i++) { 255 if (i > 0) { 256 buffer.append(", "); 257 } 258 int key = keyAt(i); 259 buffer.append(key); 260 buffer.append('='); 261 long value = valueAt(i); 262 buffer.append(value); 263 } 264 buffer.append('}'); 265 return buffer.toString(); 266 } 267} 268