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/* * #! * Ontopia Engine * #- * Copyright (C) 2001 - 2013 The Ontopia 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. * !# */ sclass CompactHashMap<K, V> extends AbstractMap<K, V> { final static int INITIAL_SIZE = 3; final static double LOAD_FACTOR = 0.6; // This object is used to represent null, should clients use that as final static Object nullObject = new Object(); /** * When a key is deleted this object is put into the hashtable in * its place, so that other entries with the same key (collisions) * further down the hashtable are not lost after we delete an object * in the collision chain. */ final static Object deletedObject = new Object(); int elements; int freecells; O[] table; // key, value, key, value, ... int modCount; *() { this(INITIAL_SIZE); } *(int size) { table = new Object[(size==0 ? 1 : size)*2]; elements = 0; freecells = tableSize(); modCount = 0; } // ===== MAP IMPLEMENTATION ============================================= /** * Returns the number of key/value mappings in this map. */ public synchronized int size() { return elements; } /** * Returns <tt>true</tt> if this map contains no mappings. */ public synchronized boolean isEmpty() { return elements == 0; } /** * Removes all key/value mappings in the map. */ public synchronized void clear() { elements = 0; for (int ix = 0; ix < tableSize(); ix++) { key(ix, null); value(ix, null); } freecells = tableSize(); modCount++; } /** * Returns <tt>true</tt> if this map contains the specified key. */ public synchronized boolean containsKey(Object k) { return key(findKeyIndex(k)) != null; } /** * Returns <tt>true</tt> if this map contains the specified value. */ public synchronized boolean containsValue(Object v) { if (v == null) v = (V)nullObject; for (int ix = 0; ix < tableSize(); ix++) if (value(ix) != null && value(ix).equals(v)) return true; return false; } /** * Returns a read-only set view of the map's keys. */ public synchronized Set<Entry<K, V>> entrySet() { throw new UnsupportedOperationException(); } /** * Removes the mapping with key k, if there is one, and returns its * value, if there is one, and null if there is none. */ public synchronized V remove(Object k) { int index = findKeyIndex(k); // we found the right position, now do the removal if (key(index) != null) { // we found the object // same problem here as with put V v = value(index); key(index, deletedObject); value(index, deletedObject); modCount++; elements--; return v; } else // we did not find the key return null; } /** * Adds the specified mapping to this map, returning the old value for * the mapping, if there was one. */ public synchronized V put(K k, V v) { if (k == null) k = (K)nullObject; int hash = k.hashCode(); int index = (hash & 0x7FFFFFFF) % tableSize(); int offset = 1; int deletedix = -1; // search for the key (continue while !null and !this key) while(key(index) != null && !(key(index).hashCode() == hash && key(index).equals(k))) { // if there's a deleted mapping here we can put this mapping here, // provided it's not in here somewhere else already if (key(index) == deletedObject) deletedix = index; index = ((index + offset) & 0x7FFFFFFF) % tableSize(); offset = offset*2 + 1; if (offset == -1) offset = 2; } if (key(index) == null) { // wasn't present already if (deletedix != -1) // reusing a deleted cell index = deletedix; else freecells--; modCount++; elements++; key(index, k); value(index, v); // rehash with increased capacity if (1 - (freecells / (double) tableSize()) > LOAD_FACTOR) rehash(tableSize()*2 + 1); return null; } else { // was there already modCount++; V oldv = value(index); value(index, v); return oldv; } } /** * INTERNAL: Rehashes the hashmap to a bigger size. */ void rehash(int newCapacity) { int oldCapacity = tableSize(); O[] newTable = new Object[newCapacity*2]; for (int ix = 0; ix < oldCapacity; ix++) { Object k = key(ix); if (k == null || k == deletedObject) continue; int hash = k.hashCode(); int index = (hash & 0x7FFFFFFF) % newCapacity; int offset = 1; // search for the key while(newTable[index*2] != null) { // no need to test for duplicates index = ((index + offset) & 0x7FFFFFFF) % newCapacity; offset = offset*2 + 1; if (offset == -1) offset = 2; } newTable[index*2] = k; newTable[index*2+1] = value(ix); } table = newTable; freecells = tableSize() - elements; } /** * Returns the value for the key k, if there is one, and null if * there is none. */ public synchronized V get(Object k) { return value(findKeyIndex(k)); } /** * Returns a virtual read-only collection containing all the values * in the map. */ public synchronized Collection<V> values() { return new ValueCollection(); } /** * Returns a virtual read-only set of all the keys in the map. */ public synchronized Set<K> keySet() { return new KeySet(); } // --- Internal utilities final int findKeyIndex(Object k) { if (k == null) k = nullObject; int hash = k.hashCode(); int index = (hash & 0x7FFFFFFF) % tableSize(); int offset = 1; // search for the key (continue while !null and !this key) while(key(index) != null && !(key(index).hashCode() == hash && key(index).equals(k))) { index = ((index + offset) & 0x7FFFFFFF) % tableSize(); offset = offset*2 + 1; if (offset == -1) offset = 2; } return index; } // --- Key set class KeySet<K> extends AbstractSet<K> { public synchronized int size() { return elements; } public synchronized boolean contains(Object k) { return containsKey(k); } public synchronized Iterator<K> iterator() { return new KeyIterator(); } } class KeyIterator<K> implements Iterator<K> { private int ix; private KeyIterator() { // walk up to first value, so that hasNext() and next() return // correct results for (; ix < tableSize(); ix++) if (value(ix) != null && key(ix) != deletedObject) break; } public synchronized boolean hasNext() { return ix < tableSize(); } public synchronized void remove() { throw new UnsupportedOperationException("Collection is read-only"); } public synchronized K next() { if (ix >= tableSize()) throw new NoSuchElementException(); K key = (K) key(ix++); // walk up to next value for (; ix < tableSize(); ix++) if (key(ix) != null && key(ix) != deletedObject) break; // ix now either points to next key, or outside array (if no next) return key; } } // --- Value collection class ValueCollection<V> extends AbstractCollection<V> { public synchronized int size() { return elements; } public synchronized Iterator<V> iterator() { return new ValueIterator(); } public synchronized boolean contains(Object v) { return containsValue(v); } } class ValueIterator<V> implements Iterator<V> { private int ix; private ValueIterator() { // walk up to first value, so that hasNext() and next() return // correct results for (; ix < table.length/2; ix++) if (value(ix) != null && value(ix) != deletedObject) break; } public synchronized boolean hasNext() { return ix < tableSize(); } public synchronized void remove() { throw new UnsupportedOperationException("Collection is read-only"); } public synchronized V next() { if (ix >= tableSize()) throw new NoSuchElementException(); V value = (V) value(ix++); // walk up to next value for (; ix < tableSize(); ix++) if (value(ix) != null && value(ix) != deletedObject) break; // ix now either points to next value, or outside array (if no next) return value; } } K key(int i) { ret (K) table[i*2]; } void key(int i, O key) { table[i*2] = key; } V value(int i) { ret (V) table[i*2+1]; } void value(int i, O value) { table[i*2+1] = value; } int tableSize() { ret table.length/2; } }
Began life as a copy of #1013303
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Snippet ID: | #1031038 |
Snippet name: | CompactHashMap - version using only one array |
Eternal ID of this version: | #1031038/8 |
Text MD5: | 5d4341d04c0a1b2b5ab7e1ce895548ae |
Transpilation MD5: | bae976d36e741ef3c53fbcf2a4815ebb |
Author: | stefan |
Category: | javax / collections |
Type: | JavaX fragment (include) |
Public (visible to everyone): | Yes |
Archived (hidden from active list): | No |
Created/modified: | 2021-04-25 21:13:47 |
Source code size: | 9757 bytes / 370 lines |
Pitched / IR pitched: | No / No |
Views / Downloads: | 166 / 241 |
Version history: | 7 change(s) |
Referenced in: | #1031040 - CompactHashMap - using only one array, no modCount. synchronized |