Java tutorial
/* * Copyright (C) 2006 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package android.util; import com.android.internal.util.ArrayUtils; import com.android.internal.util.GrowingArrayUtils; import java.util.Arrays; import android.annotation.UnsupportedAppUsage; import libcore.util.EmptyArray; /** * SparseIntArrays map integers to integers. Unlike a normal array of integers, * there can be gaps in the indices. It is intended to be more memory efficient * than using a HashMap to map Integers to Integers, both because it avoids * auto-boxing keys and values and its data structure doesn't rely on an extra entry object * for each mapping. * * <p>Note that this container keeps its mappings in an array data structure, * using a binary search to find keys. The implementation is not intended to be appropriate for * data structures * that may contain large numbers of items. It is generally slower than a traditional * HashMap, since lookups require a binary search and adds and removes require inserting * and deleting entries in the array. For containers holding up to hundreds of items, * the performance difference is not significant, less than 50%.</p> * * <p>It is possible to iterate over the items in this container using * {@link #keyAt(int)} and {@link #valueAt(int)}. Iterating over the keys using * <code>keyAt(int)</code> with ascending values of the index will return the * keys in ascending order, or the values corresponding to the keys in ascending * order in the case of <code>valueAt(int)</code>.</p> */ public class SparseIntArray implements Cloneable { @UnsupportedAppUsage private int[] mKeys; @UnsupportedAppUsage private int[] mValues; @UnsupportedAppUsage private int mSize; /** * Creates a new SparseIntArray containing no mappings. */ public SparseIntArray() { this(10); } /** * Creates a new SparseIntArray containing no mappings that will not * require any additional memory allocation to store the specified * number of mappings. If you supply an initial capacity of 0, the * sparse array will be initialized with a light-weight representation * not requiring any additional array allocations. */ public SparseIntArray(int initialCapacity) { if (initialCapacity == 0) { mKeys = EmptyArray.INT; mValues = EmptyArray.INT; } else { mKeys = ArrayUtils.newUnpaddedIntArray(initialCapacity); mValues = new int[mKeys.length]; } mSize = 0; } @Override public SparseIntArray clone() { SparseIntArray clone = null; try { clone = (SparseIntArray) super.clone(); clone.mKeys = mKeys.clone(); clone.mValues = mValues.clone(); } catch (CloneNotSupportedException cnse) { /* ignore */ } return clone; } /** * Gets the int mapped from the specified key, or <code>0</code> * if no such mapping has been made. */ public int get(int key) { return get(key, 0); } /** * Gets the int mapped from the specified key, or the specified value * if no such mapping has been made. */ public int get(int key, int valueIfKeyNotFound) { int i = ContainerHelpers.binarySearch(mKeys, mSize, key); if (i < 0) { return valueIfKeyNotFound; } else { return mValues[i]; } } /** * Removes the mapping from the specified key, if there was any. */ public void delete(int key) { int i = ContainerHelpers.binarySearch(mKeys, mSize, key); if (i >= 0) { removeAt(i); } } /** * Removes the mapping at the given index. */ public void removeAt(int index) { System.arraycopy(mKeys, index + 1, mKeys, index, mSize - (index + 1)); System.arraycopy(mValues, index + 1, mValues, index, mSize - (index + 1)); mSize--; } /** * Adds a mapping from the specified key to the specified value, * replacing the previous mapping from the specified key if there * was one. */ public void put(int key, int value) { int i = ContainerHelpers.binarySearch(mKeys, mSize, key); if (i >= 0) { mValues[i] = value; } else { i = ~i; mKeys = GrowingArrayUtils.insert(mKeys, mSize, i, key); mValues = GrowingArrayUtils.insert(mValues, mSize, i, value); mSize++; } } /** * Returns the number of key-value mappings that this SparseIntArray * currently stores. */ public int size() { return mSize; } /** * Given an index in the range <code>0...size()-1</code>, returns * the key from the <code>index</code>th key-value mapping that this * SparseIntArray stores. * * <p>The keys corresponding to indices in ascending order are guaranteed to * be in ascending order, e.g., <code>keyAt(0)</code> will return the * smallest key and <code>keyAt(size()-1)</code> will return the largest * key.</p> */ public int keyAt(int index) { return mKeys[index]; } /** * Given an index in the range <code>0...size()-1</code>, returns * the value from the <code>index</code>th key-value mapping that this * SparseIntArray stores. * * <p>The values corresponding to indices in ascending order are guaranteed * to be associated with keys in ascending order, e.g., * <code>valueAt(0)</code> will return the value associated with the * smallest key and <code>valueAt(size()-1)</code> will return the value * associated with the largest key.</p> */ public int valueAt(int index) { return mValues[index]; } /** * Directly set the value at a particular index. * @hide */ public void setValueAt(int index, int value) { mValues[index] = value; } /** * Returns the index for which {@link #keyAt} would return the * specified key, or a negative number if the specified * key is not mapped. */ public int indexOfKey(int key) { return ContainerHelpers.binarySearch(mKeys, mSize, key); } /** * Returns an index for which {@link #valueAt} would return the * specified key, or a negative number if no keys map to the * specified value. * Beware that this is a linear search, unlike lookups by key, * and that multiple keys can map to the same value and this will * find only one of them. */ public int indexOfValue(int value) { for (int i = 0; i < mSize; i++) if (mValues[i] == value) return i; return -1; } /** * Removes all key-value mappings from this SparseIntArray. */ public void clear() { mSize = 0; } /** * Puts a key/value pair into the array, optimizing for the case where * the key is greater than all existing keys in the array. */ public void append(int key, int value) { if (mSize != 0 && key <= mKeys[mSize - 1]) { put(key, value); return; } mKeys = GrowingArrayUtils.append(mKeys, mSize, key); mValues = GrowingArrayUtils.append(mValues, mSize, value); mSize++; } /** * Provides a copy of keys. * * @hide * */ public int[] copyKeys() { if (size() == 0) { return null; } return Arrays.copyOf(mKeys, size()); } /** * {@inheritDoc} * * <p>This implementation composes a string by iterating over its mappings. */ @Override public String toString() { if (size() <= 0) { return "{}"; } StringBuilder buffer = new StringBuilder(mSize * 28); buffer.append('{'); for (int i = 0; i < mSize; i++) { if (i > 0) { buffer.append(", "); } int key = keyAt(i); buffer.append(key); buffer.append('='); int value = valueAt(i); buffer.append(value); } buffer.append('}'); return buffer.toString(); } }