Java tutorial
/* * Copyright (C) 2009 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 libcore.util.EmptyArray; /** * SparseArray mapping longs to Objects. Unlike a normal array of Objects, * there can be gaps in the indices. It is intended to be more memory efficient * than using a HashMap to map Longs to Objects, both because it avoids * auto-boxing keys 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>To help with performance, the container includes an optimization when removing * keys: instead of compacting its array immediately, it leaves the removed entry marked * as deleted. The entry can then be re-used for the same key, or compacted later in * a single garbage collection step of all removed entries. This garbage collection will * need to be performed at any time the array needs to be grown or the the map size or * entry values are retrieved.</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 LongSparseArray<E> implements Cloneable { private static final Object DELETED = new Object(); private boolean mGarbage = false; private long[] mKeys; private Object[] mValues; private int mSize; /** * Creates a new LongSparseArray containing no mappings. */ public LongSparseArray() { this(10); } /** * Creates a new LongSparseArray 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 LongSparseArray(int initialCapacity) { if (initialCapacity == 0) { mKeys = EmptyArray.LONG; mValues = EmptyArray.OBJECT; } else { mKeys = ArrayUtils.newUnpaddedLongArray(initialCapacity); mValues = ArrayUtils.newUnpaddedObjectArray(initialCapacity); } mSize = 0; } @Override @SuppressWarnings("unchecked") public LongSparseArray<E> clone() { LongSparseArray<E> clone = null; try { clone = (LongSparseArray<E>) super.clone(); clone.mKeys = mKeys.clone(); clone.mValues = mValues.clone(); } catch (CloneNotSupportedException cnse) { /* ignore */ } return clone; } /** * Gets the Object mapped from the specified key, or <code>null</code> * if no such mapping has been made. */ public E get(long key) { return get(key, null); } /** * Gets the Object mapped from the specified key, or the specified Object * if no such mapping has been made. */ @SuppressWarnings("unchecked") public E get(long key, E valueIfKeyNotFound) { int i = ContainerHelpers.binarySearch(mKeys, mSize, key); if (i < 0 || mValues[i] == DELETED) { return valueIfKeyNotFound; } else { return (E) mValues[i]; } } /** * Removes the mapping from the specified key, if there was any. */ public void delete(long key) { int i = ContainerHelpers.binarySearch(mKeys, mSize, key); if (i >= 0) { if (mValues[i] != DELETED) { mValues[i] = DELETED; mGarbage = true; } } } /** * Alias for {@link #delete(long)}. */ public void remove(long key) { delete(key); } /** * Removes the mapping at the specified index. */ public void removeAt(int index) { if (mValues[index] != DELETED) { mValues[index] = DELETED; mGarbage = true; } } private void gc() { // Log.e("SparseArray", "gc start with " + mSize); int n = mSize; int o = 0; long[] keys = mKeys; Object[] values = mValues; for (int i = 0; i < n; i++) { Object val = values[i]; if (val != DELETED) { if (i != o) { keys[o] = keys[i]; values[o] = val; values[i] = null; } o++; } } mGarbage = false; mSize = o; // Log.e("SparseArray", "gc end with " + 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(long key, E value) { int i = ContainerHelpers.binarySearch(mKeys, mSize, key); if (i >= 0) { mValues[i] = value; } else { i = ~i; if (i < mSize && mValues[i] == DELETED) { mKeys[i] = key; mValues[i] = value; return; } if (mGarbage && mSize >= mKeys.length) { gc(); // Search again because indices may have changed. i = ~ContainerHelpers.binarySearch(mKeys, mSize, key); } mKeys = GrowingArrayUtils.insert(mKeys, mSize, i, key); mValues = GrowingArrayUtils.insert(mValues, mSize, i, value); mSize++; } } /** * Returns the number of key-value mappings that this LongSparseArray * currently stores. */ public int size() { if (mGarbage) { gc(); } 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 * LongSparseArray 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 long keyAt(int index) { if (mGarbage) { gc(); } 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 * LongSparseArray 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> */ @SuppressWarnings("unchecked") public E valueAt(int index) { if (mGarbage) { gc(); } return (E) mValues[index]; } /** * Given an index in the range <code>0...size()-1</code>, sets a new * value for the <code>index</code>th key-value mapping that this * LongSparseArray stores. */ public void setValueAt(int index, E value) { if (mGarbage) { gc(); } 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(long key) { if (mGarbage) { gc(); } 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(E value) { if (mGarbage) { gc(); } for (int i = 0; i < mSize; i++) { if (mValues[i] == value) { return i; } } return -1; } /** * Returns an index for which {@link #valueAt} would return the * specified key, or a negative number if no keys map to the * specified value. * <p>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. * <p>Note also that this method uses {@code equals} unlike {@code indexOfValue}. * @hide */ public int indexOfValueByValue(E value) { if (mGarbage) { gc(); } for (int i = 0; i < mSize; i++) { if (value == null) { if (mValues[i] == null) { return i; } } else { if (value.equals(mValues[i])) { return i; } } } return -1; } /** * Removes all key-value mappings from this LongSparseArray. */ public void clear() { int n = mSize; Object[] values = mValues; for (int i = 0; i < n; i++) { values[i] = null; } mSize = 0; mGarbage = false; } /** * 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(long key, E value) { if (mSize != 0 && key <= mKeys[mSize - 1]) { put(key, value); return; } if (mGarbage && mSize >= mKeys.length) { gc(); } mKeys = GrowingArrayUtils.append(mKeys, mSize, key); mValues = GrowingArrayUtils.append(mValues, mSize, value); mSize++; } /** * {@inheritDoc} * * <p>This implementation composes a string by iterating over its mappings. If * this map contains itself as a value, the string "(this Map)" * will appear in its place. */ @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(", "); } long key = keyAt(i); buffer.append(key); buffer.append('='); Object value = valueAt(i); if (value != this) { buffer.append(value); } else { buffer.append("(this Map)"); } } buffer.append('}'); return buffer.toString(); } }