Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You 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 org.apache.commons.math3.util; import java.io.IOException; import java.io.ObjectInputStream; import java.io.Serializable; import java.util.ConcurrentModificationException; import java.util.NoSuchElementException; /** * Open addressed map from int to double. * <p>This class provides a dedicated map from integers to doubles with a * much smaller memory overhead than standard <code>java.util.Map</code>.</p> * <p>This class is not synchronized. The specialized iterators returned by * {@link #iterator()} are fail-fast: they throw a * <code>ConcurrentModificationException</code> when they detect the map has been * modified during iteration.</p> * @version $Id: OpenIntToDoubleHashMap.java 1421448 2012-12-13 19:45:57Z tn $ * @since 2.0 */ public class OpenIntToDoubleHashMap implements Serializable { /** Status indicator for free table entries. */ protected static final byte FREE = 0; /** Status indicator for full table entries. */ protected static final byte FULL = 1; /** Status indicator for removed table entries. */ protected static final byte REMOVED = 2; /** Serializable version identifier */ private static final long serialVersionUID = -3646337053166149105L; /** Load factor for the map. */ private static final float LOAD_FACTOR = 0.5f; /** Default starting size. * <p>This must be a power of two for bit mask to work properly. </p> */ private static final int DEFAULT_EXPECTED_SIZE = 16; /** Multiplier for size growth when map fills up. * <p>This must be a power of two for bit mask to work properly. </p> */ private static final int RESIZE_MULTIPLIER = 2; /** Number of bits to perturb the index when probing for collision resolution. */ private static final int PERTURB_SHIFT = 5; /** Keys table. */ private int[] keys; /** Values table. */ private double[] values; /** States table. */ private byte[] states; /** Return value for missing entries. */ private final double missingEntries; /** Current size of the map. */ private int size; /** Bit mask for hash values. */ private int mask; /** Modifications count. */ private transient int count; /** * Build an empty map with default size and using NaN for missing entries. */ public OpenIntToDoubleHashMap() { this(DEFAULT_EXPECTED_SIZE, Double.NaN); } /** * Build an empty map with default size * @param missingEntries value to return when a missing entry is fetched */ public OpenIntToDoubleHashMap(final double missingEntries) { this(DEFAULT_EXPECTED_SIZE, missingEntries); } /** * Build an empty map with specified size and using NaN for missing entries. * @param expectedSize expected number of elements in the map */ public OpenIntToDoubleHashMap(final int expectedSize) { this(expectedSize, Double.NaN); } /** * Build an empty map with specified size. * @param expectedSize expected number of elements in the map * @param missingEntries value to return when a missing entry is fetched */ public OpenIntToDoubleHashMap(final int expectedSize, final double missingEntries) { final int capacity = computeCapacity(expectedSize); keys = new int[capacity]; values = new double[capacity]; states = new byte[capacity]; this.missingEntries = missingEntries; mask = capacity - 1; } /** * Copy constructor. * @param source map to copy */ public OpenIntToDoubleHashMap(final OpenIntToDoubleHashMap source) { final int length = source.keys.length; keys = new int[length]; System.arraycopy(source.keys, 0, keys, 0, length); values = new double[length]; System.arraycopy(source.values, 0, values, 0, length); states = new byte[length]; System.arraycopy(source.states, 0, states, 0, length); missingEntries = source.missingEntries; size = source.size; mask = source.mask; count = source.count; } /** * Compute the capacity needed for a given size. * @param expectedSize expected size of the map * @return capacity to use for the specified size */ private static int computeCapacity(final int expectedSize) { if (expectedSize == 0) { return 1; } final int capacity = (int) FastMath.ceil(expectedSize / LOAD_FACTOR); final int powerOfTwo = Integer.highestOneBit(capacity); if (powerOfTwo == capacity) { return capacity; } return nextPowerOfTwo(capacity); } /** * Find the smallest power of two greater than the input value * @param i input value * @return smallest power of two greater than the input value */ private static int nextPowerOfTwo(final int i) { return Integer.highestOneBit(i) << 1; } /** * Get the stored value associated with the given key * @param key key associated with the data * @return data associated with the key */ public double get(final int key) { final int hash = hashOf(key); int index = hash & mask; if (containsKey(key, index)) { return values[index]; } if (states[index] == FREE) { return missingEntries; } int j = index; for (int perturb = perturb(hash); states[index] != FREE; perturb >>= PERTURB_SHIFT) { j = probe(perturb, j); index = j & mask; if (containsKey(key, index)) { return values[index]; } } return missingEntries; } /** * Check if a value is associated with a key. * @param key key to check * @return true if a value is associated with key */ public boolean containsKey(final int key) { final int hash = hashOf(key); int index = hash & mask; if (containsKey(key, index)) { return true; } if (states[index] == FREE) { return false; } int j = index; for (int perturb = perturb(hash); states[index] != FREE; perturb >>= PERTURB_SHIFT) { j = probe(perturb, j); index = j & mask; if (containsKey(key, index)) { return true; } } return false; } /** * Get an iterator over map elements. * <p>The specialized iterators returned are fail-fast: they throw a * <code>ConcurrentModificationException</code> when they detect the map * has been modified during iteration.</p> * @return iterator over the map elements */ public Iterator iterator() { return new Iterator(); } /** * Perturb the hash for starting probing. * @param hash initial hash * @return perturbed hash */ private static int perturb(final int hash) { return hash & 0x7fffffff; } /** * Find the index at which a key should be inserted * @param key key to lookup * @return index at which key should be inserted */ private int findInsertionIndex(final int key) { return findInsertionIndex(keys, states, key, mask); } /** * Find the index at which a key should be inserted * @param keys keys table * @param states states table * @param key key to lookup * @param mask bit mask for hash values * @return index at which key should be inserted */ private static int findInsertionIndex(final int[] keys, final byte[] states, final int key, final int mask) { final int hash = hashOf(key); int index = hash & mask; if (states[index] == FREE) { return index; } else if (states[index] == FULL && keys[index] == key) { return changeIndexSign(index); } int perturb = perturb(hash); int j = index; if (states[index] == FULL) { while (true) { j = probe(perturb, j); index = j & mask; perturb >>= PERTURB_SHIFT; if (states[index] != FULL || keys[index] == key) { break; } } } if (states[index] == FREE) { return index; } else if (states[index] == FULL) { // due to the loop exit condition, // if (states[index] == FULL) then keys[index] == key return changeIndexSign(index); } final int firstRemoved = index; while (true) { j = probe(perturb, j); index = j & mask; if (states[index] == FREE) { return firstRemoved; } else if (states[index] == FULL && keys[index] == key) { return changeIndexSign(index); } perturb >>= PERTURB_SHIFT; } } /** * Compute next probe for collision resolution * @param perturb perturbed hash * @param j previous probe * @return next probe */ private static int probe(final int perturb, final int j) { return (j << 2) + j + perturb + 1; } /** * Change the index sign * @param index initial index * @return changed index */ private static int changeIndexSign(final int index) { return -index - 1; } /** * Get the number of elements stored in the map. * @return number of elements stored in the map */ public int size() { return size; } /** * Remove the value associated with a key. * @param key key to which the value is associated * @return removed value */ public double remove(final int key) { final int hash = hashOf(key); int index = hash & mask; if (containsKey(key, index)) { return doRemove(index); } if (states[index] == FREE) { return missingEntries; } int j = index; for (int perturb = perturb(hash); states[index] != FREE; perturb >>= PERTURB_SHIFT) { j = probe(perturb, j); index = j & mask; if (containsKey(key, index)) { return doRemove(index); } } return missingEntries; } /** * Check if the tables contain an element associated with specified key * at specified index. * @param key key to check * @param index index to check * @return true if an element is associated with key at index */ private boolean containsKey(final int key, final int index) { return (key != 0 || states[index] == FULL) && keys[index] == key; } /** * Remove an element at specified index. * @param index index of the element to remove * @return removed value */ private double doRemove(int index) { keys[index] = 0; states[index] = REMOVED; final double previous = values[index]; values[index] = missingEntries; --size; ++count; return previous; } /** * Put a value associated with a key in the map. * @param key key to which value is associated * @param value value to put in the map * @return previous value associated with the key */ public double put(final int key, final double value) { int index = findInsertionIndex(key); double previous = missingEntries; boolean newMapping = true; if (index < 0) { index = changeIndexSign(index); previous = values[index]; newMapping = false; } keys[index] = key; states[index] = FULL; values[index] = value; if (newMapping) { ++size; if (shouldGrowTable()) { growTable(); } ++count; } return previous; } /** * Grow the tables. */ private void growTable() { final int oldLength = states.length; final int[] oldKeys = keys; final double[] oldValues = values; final byte[] oldStates = states; final int newLength = RESIZE_MULTIPLIER * oldLength; final int[] newKeys = new int[newLength]; final double[] newValues = new double[newLength]; final byte[] newStates = new byte[newLength]; final int newMask = newLength - 1; for (int i = 0; i < oldLength; ++i) { if (oldStates[i] == FULL) { final int key = oldKeys[i]; final int index = findInsertionIndex(newKeys, newStates, key, newMask); newKeys[index] = key; newValues[index] = oldValues[i]; newStates[index] = FULL; } } mask = newMask; keys = newKeys; values = newValues; states = newStates; } /** * Check if tables should grow due to increased size. * @return true if tables should grow */ private boolean shouldGrowTable() { return size > (mask + 1) * LOAD_FACTOR; } /** * Compute the hash value of a key * @param key key to hash * @return hash value of the key */ private static int hashOf(final int key) { final int h = key ^ ((key >>> 20) ^ (key >>> 12)); return h ^ (h >>> 7) ^ (h >>> 4); } /** Iterator class for the map. */ public class Iterator { /** Reference modification count. */ private final int referenceCount; /** Index of current element. */ private int current; /** Index of next element. */ private int next; /** * Simple constructor. */ private Iterator() { // preserve the modification count of the map to detect concurrent modifications later referenceCount = count; // initialize current index next = -1; try { advance(); } catch (NoSuchElementException nsee) { // NOPMD // ignored } } /** * Check if there is a next element in the map. * @return true if there is a next element */ public boolean hasNext() { return next >= 0; } /** * Get the key of current entry. * @return key of current entry * @exception ConcurrentModificationException if the map is modified during iteration * @exception NoSuchElementException if there is no element left in the map */ public int key() throws ConcurrentModificationException, NoSuchElementException { if (referenceCount != count) { throw new ConcurrentModificationException(); } if (current < 0) { throw new NoSuchElementException(); } return keys[current]; } /** * Get the value of current entry. * @return value of current entry * @exception ConcurrentModificationException if the map is modified during iteration * @exception NoSuchElementException if there is no element left in the map */ public double value() throws ConcurrentModificationException, NoSuchElementException { if (referenceCount != count) { throw new ConcurrentModificationException(); } if (current < 0) { throw new NoSuchElementException(); } return values[current]; } /** * Advance iterator one step further. * @exception ConcurrentModificationException if the map is modified during iteration * @exception NoSuchElementException if there is no element left in the map */ public void advance() throws ConcurrentModificationException, NoSuchElementException { if (referenceCount != count) { throw new ConcurrentModificationException(); } // advance on step current = next; // prepare next step try { while (states[++next] != FULL) { // NOPMD // nothing to do } } catch (ArrayIndexOutOfBoundsException e) { next = -2; if (current < 0) { throw new NoSuchElementException(); } } } } /** * Read a serialized object. * @param stream input stream * @throws IOException if object cannot be read * @throws ClassNotFoundException if the class corresponding * to the serialized object cannot be found */ private void readObject(final ObjectInputStream stream) throws IOException, ClassNotFoundException { stream.defaultReadObject(); count = 0; } }