Java tutorial
/* * $Id: ArrayListStack.java 4448 2006-02-14 20:54:57Z jonathanlocke $ $Revision: * 4448 $ $Date: 2006-02-14 21:54:57 +0100 (di, 14 feb 2006) $ * * * 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. */ import java.io.IOException; import java.io.Serializable; import java.util.AbstractCollection; import java.util.AbstractSet; import java.util.Collection; import java.util.ConcurrentModificationException; import java.util.Iterator; import java.util.Map; import java.util.NoSuchElementException; import java.util.Set; /** * This is a int hashmap that has the exact same features and interface as a * normal Map except that the key is directly an integer. So no hash is * calculated or key object is stored. * * @author jcompagner */ public class IntHashMap implements Cloneable, Serializable { transient volatile Set keySet = null; transient volatile Collection values = null; /** * The default initial capacity - MUST be a power of two. */ static final int DEFAULT_INITIAL_CAPACITY = 16; /** * The maximum capacity, used if a higher value is implicitly specified by * either of the constructors with arguments. MUST be a power of two <= 1<<30. */ static final int MAXIMUM_CAPACITY = 1 << 30; /** * The load factor used when none specified in constructor. */ static final float DEFAULT_LOAD_FACTOR = 0.75f; /** * The table, resized as necessary. Length MUST Always be a power of two. */ transient Entry[] table; /** * The number of key-value mappings contained in this identity hash map. */ transient int size; /** * The next size value at which to resize (capacity * load factor). * * @serial */ int threshold; /** * The load factor for the hash table. * * @serial */ final float loadFactor; /** * The number of times this HashMap has been structurally modified * Structural modifications are those that change the number of mappings in * the HashMap or otherwise modify its internal structure (e.g., rehash). * This field is used to make iterators on Collection-views of the HashMap * fail-fast. (See ConcurrentModificationException). */ transient volatile int modCount; /** * Constructs an empty <tt>HashMap</tt> with the specified initial * capacity and load factor. * * @param initialCapacity * The initial capacity. * @param loadFactor * The load factor. * @throws IllegalArgumentException * if the initial capacity is negative or the load factor is * nonpositive. */ public IntHashMap(int initialCapacity, float loadFactor) { if (initialCapacity < 0) { throw new IllegalArgumentException("Illegal initial capacity: " + //$NON-NLS-1$ initialCapacity); } if (initialCapacity > MAXIMUM_CAPACITY) { initialCapacity = MAXIMUM_CAPACITY; } if (loadFactor <= 0 || Float.isNaN(loadFactor)) { throw new IllegalArgumentException("Illegal load factor: " + //$NON-NLS-1$ loadFactor); } // Find a power of 2 >= initialCapacity int capacity = 1; while (capacity < initialCapacity) { capacity <<= 1; } this.loadFactor = loadFactor; threshold = (int) (capacity * loadFactor); table = new Entry[capacity]; init(); } /** * Constructs an empty <tt>HashMap</tt> with the specified initial * capacity and the default load factor (0.75). * * @param initialCapacity * the initial capacity. * @throws IllegalArgumentException * if the initial capacity is negative. */ public IntHashMap(int initialCapacity) { this(initialCapacity, DEFAULT_LOAD_FACTOR); } /** * Constructs an empty <tt>HashMap</tt> with the default initial capacity * (16) and the default load factor (0.75). */ public IntHashMap() { this.loadFactor = DEFAULT_LOAD_FACTOR; threshold = (int) (DEFAULT_INITIAL_CAPACITY * DEFAULT_LOAD_FACTOR); table = new Entry[DEFAULT_INITIAL_CAPACITY]; init(); } // internal utilities /** * Initialization hook for subclasses. This method is called in all * constructors and pseudo-constructors (clone, readObject) after HashMap * has been initialized but before any entries have been inserted. (In the * absence of this method, readObject would require explicit knowledge of * subclasses.) */ void init() { } /** * Returns index for hash code h. * * @param h * @param length * @return The index for the hash integer for the given length */ static int indexFor(int h, int length) { return h & (length - 1); } /** * Returns the number of key-value mappings in this map. * * @return the number of key-value mappings in this map. */ public int size() { return size; } /** * Returns <tt>true</tt> if this map contains no key-value mappings. * * @return <tt>true</tt> if this map contains no key-value mappings. */ public boolean isEmpty() { return size == 0; } /** * Returns the value to which the specified key is mapped in this identity * hash map, or <tt>null</tt> if the map contains no mapping for this key. * A return value of <tt>null</tt> does not <i>necessarily</i> indicate * that the map contains no mapping for the key; it is also possible that * the map explicitly maps the key to <tt>null</tt>. The * <tt>containsKey</tt> method may be used to distinguish these two cases. * * @param key * the key whose associated value is to be returned. * @return the value to which this map maps the specified key, or * <tt>null</tt> if the map contains no mapping for this key. * @see #put(int, Object) */ public Object get(int key) { int i = indexFor(key, table.length); Entry e = table[i]; while (true) { if (e == null) { return e; } if (key == e.key) { return e.value; } e = e.next; } } /** * Returns <tt>true</tt> if this map contains a mapping for the specified * key. * * @param key * The key whose presence in this map is to be tested * @return <tt>true</tt> if this map contains a mapping for the specified * key. */ public boolean containsKey(int key) { int i = indexFor(key, table.length); Entry e = table[i]; while (e != null) { if (key == e.key) { return true; } e = e.next; } return false; } /** * Returns the entry associated with the specified key in the HashMap. * Returns null if the HashMap contains no mapping for this key. * * @param key * @return The Entry object for the given hash key */ Entry getEntry(int key) { int i = indexFor(key, table.length); Entry e = table[i]; while (e != null && !(key == e.key)) { e = e.next; } return e; } /** * Associates the specified value with the specified key in this map. If the * map previously contained a mapping for this key, the old value is * replaced. * * @param key * key with which the specified value is to be associated. * @param value * value to be associated with the specified key. * @return previous value associated with specified key, or <tt>null</tt> * if there was no mapping for key. A <tt>null</tt> return can * also indicate that the HashMap previously associated * <tt>null</tt> with the specified key. */ public Object put(int key, Object value) { int i = indexFor(key, table.length); for (Entry e = table[i]; e != null; e = e.next) { if (key == e.key) { Object oldValue = e.value; e.value = value; return oldValue; } } modCount++; addEntry(key, value, i); return null; } /** * This method is used instead of put by constructors and pseudoconstructors * (clone, readObject). It does not resize the table, check for * comodification, etc. It calls createEntry rather than addEntry. * * @param key * @param value */ private void putForCreate(int key, Object value) { int i = indexFor(key, table.length); /** * Look for preexisting entry for key. This will never happen for clone * or deserialize. It will only happen for construction if the input Map * is a sorted map whose ordering is inconsistent w/ equals. */ for (Entry e = table[i]; e != null; e = e.next) { if (key == e.key) { e.value = value; return; } } createEntry(key, value, i); } void putAllForCreate(IntHashMap m) { for (Iterator i = m.entrySet().iterator(); i.hasNext();) { Entry e = (Entry) i.next(); putForCreate(e.getKey(), e.getValue()); } } /** * Rehashes the contents of this map into a new array with a larger * capacity. This method is called automatically when the number of keys in * this map reaches its threshold. * * If current capacity is MAXIMUM_CAPACITY, this method does not resize the * map, but but sets threshold to Integer.MAX_VALUE. This has the effect of * preventing future calls. * * @param newCapacity * the new capacity, MUST be a power of two; must be greater than * current capacity unless current capacity is MAXIMUM_CAPACITY * (in which case value is irrelevant). */ void resize(int newCapacity) { Entry[] oldTable = table; int oldCapacity = oldTable.length; if (oldCapacity == MAXIMUM_CAPACITY) { threshold = Integer.MAX_VALUE; return; } Entry[] newTable = new Entry[newCapacity]; transfer(newTable); table = newTable; threshold = (int) (newCapacity * loadFactor); } /** * Transfer all entries from current table to newTable. * * @param newTable */ void transfer(Entry[] newTable) { Entry[] src = table; int newCapacity = newTable.length; for (int j = 0; j < src.length; j++) { Entry e = src[j]; if (e != null) { src[j] = null; do { Entry next = e.next; int i = indexFor(e.key, newCapacity); e.next = newTable[i]; newTable[i] = e; e = next; } while (e != null); } } } /** * Copies all of the mappings from the specified map to this map These * mappings will replace any mappings that this map had for any of the keys * currently in the specified map. * * @param m * mappings to be stored in this map. * @throws NullPointerException * if the specified map is null. */ public void putAll(IntHashMap m) { int numKeysToBeAdded = m.size(); if (numKeysToBeAdded == 0) { return; } /* * Expand the map if the map if the number of mappings to be added is * greater than or equal to threshold. This is conservative; the obvious * condition is (m.size() + size) >= threshold, but this condition could * result in a map with twice the appropriate capacity, if the keys to * be added overlap with the keys already in this map. By using the * conservative calculation, we subject ourself to at most one extra * resize. */ if (numKeysToBeAdded > threshold) { int targetCapacity = (int) (numKeysToBeAdded / loadFactor + 1); if (targetCapacity > MAXIMUM_CAPACITY) { targetCapacity = MAXIMUM_CAPACITY; } int newCapacity = table.length; while (newCapacity < targetCapacity) { newCapacity <<= 1; } if (newCapacity > table.length) { resize(newCapacity); } } for (Iterator i = m.entrySet().iterator(); i.hasNext();) { Entry e = (Entry) i.next(); put(e.getKey(), e.getValue()); } } /** * Removes the mapping for this key from this map if present. * * @param key * key whose mapping is to be removed from the map. * @return previous value associated with specified key, or <tt>null</tt> * if there was no mapping for key. A <tt>null</tt> return can * also indicate that the map previously associated <tt>null</tt> * with the specified key. */ public Object remove(int key) { Entry e = removeEntryForKey(key); return (e == null ? e : e.value); } /** * Removes and returns the entry associated with the specified key in the * HashMap. Returns null if the HashMap contains no mapping for this key. * * @param key * @return The Entry object that was removed */ Entry removeEntryForKey(int key) { int i = indexFor(key, table.length); Entry prev = table[i]; Entry e = prev; while (e != null) { Entry next = e.next; if (key == e.key) { modCount++; size--; if (prev == e) { table[i] = next; } else { prev.next = next; } return e; } prev = e; e = next; } return e; } /** * Special version of remove for EntrySet. * * @param o * @return The entry that was removed */ Entry removeMapping(Object o) { if (!(o instanceof Entry)) { return null; } Entry entry = (Entry) o; int key = entry.getKey(); int i = indexFor(key, table.length); Entry prev = table[i]; Entry e = prev; while (e != null) { Entry next = e.next; if (e.key == key && e.equals(entry)) { modCount++; size--; if (prev == e) { table[i] = next; } else { prev.next = next; } return e; } prev = e; e = next; } return e; } /** * Removes all mappings from this map. */ public void clear() { modCount++; Entry tab[] = table; for (int i = 0; i < tab.length; i++) { tab[i] = null; } size = 0; } /** * Returns <tt>true</tt> if this map maps one or more keys to the * specified value. * * @param value * value whose presence in this map is to be tested. * @return <tt>true</tt> if this map maps one or more keys to the * specified value. */ public boolean containsValue(Object value) { if (value == null) { return containsNullValue(); } Entry tab[] = table; for (int i = 0; i < tab.length; i++) { for (Entry e = tab[i]; e != null; e = e.next) { if (value.equals(e.value)) { return true; } } } return false; } /** * Special-case code for containsValue with null argument * * @return boolean true if there is a null value in this map */ private boolean containsNullValue() { Entry tab[] = table; for (int i = 0; i < tab.length; i++) { for (Entry e = tab[i]; e != null; e = e.next) { if (e.value == null) { return true; } } } return false; } /** * Returns a shallow copy of this <tt>HashMap</tt> instance: the keys and * values themselves are not cloned. * * @return a shallow copy of this map. */ public Object clone() throws CloneNotSupportedException { IntHashMap result = null; try { result = (IntHashMap) super.clone(); result.table = new Entry[table.length]; result.entrySet = null; result.modCount = 0; result.size = 0; result.init(); result.putAllForCreate(this); } catch (CloneNotSupportedException e) { // assert false; } return result; } /** * @author jcompagner */ public static class Entry { final int key; Object value; Entry next; /** * Create new entry. * * @param k * @param v * @param n */ Entry(int k, Object v, Entry n) { value = v; next = n; key = k; } /** * @return The int key of this entry */ public int getKey() { return key; } /** * @return Gets the value object of this entry */ public Object getValue() { return value; } /** * @param newValue * @return The previous value */ public Object setValue(Object newValue) { Object oldValue = value; value = newValue; return oldValue; } /** * @see java.lang.Object#equals(java.lang.Object) */ public boolean equals(Object o) { if (!(o instanceof Entry)) { return false; } Entry e = (Entry) o; int k1 = getKey(); int k2 = e.getKey(); if (k1 == k2) { Object v1 = getValue(); Object v2 = e.getValue(); if (v1 == v2 || (v1 != null && v1.equals(v2))) { return true; } } return false; } /** * @see java.lang.Object#hashCode() */ public int hashCode() { return key ^ (value == null ? 0 : value.hashCode()); } /** * @see java.lang.Object#toString() */ public String toString() { return getKey() + "=" + getValue(); //$NON-NLS-1$ } } /** * Add a new entry with the specified key, value and hash code to the * specified bucket. It is the responsibility of this method to resize the * table if appropriate. * * Subclass overrides this to alter the behavior of put method. * * @param key * @param value * @param bucketIndex */ void addEntry(int key, Object value, int bucketIndex) { table[bucketIndex] = new Entry(key, value, table[bucketIndex]); if (size++ >= threshold) { resize(2 * table.length); } } /** * Like addEntry except that this version is used when creating entries as * part of Map construction or "pseudo-construction" (cloning, * deserialization). This version needn't worry about resizing the table. * * Subclass overrides this to alter the behavior of HashMap(Map), clone, and * readObject. * * @param key * @param value * @param bucketIndex */ void createEntry(int key, Object value, int bucketIndex) { table[bucketIndex] = new Entry(key, value, table[bucketIndex]); size++; } private abstract class HashIterator implements Iterator { Entry next; // next entry to return int expectedModCount; // For fast-fail int index; // current slot Entry current; // current entry HashIterator() { expectedModCount = modCount; Entry[] t = table; int i = t.length; Entry n = null; if (size != 0) { // advance to first entry while (i > 0 && (n = t[--i]) == null) { /* NoOp*/ ; } } next = n; index = i; } /** * @see java.util.Iterator#hasNext() */ public boolean hasNext() { return next != null; } Entry nextEntry() { if (modCount != expectedModCount) { throw new ConcurrentModificationException(); } Entry e = next; if (e == null) { throw new NoSuchElementException(); } Entry n = e.next; Entry[] t = table; int i = index; while (n == null && i > 0) { n = t[--i]; } index = i; next = n; return current = e; } /** * @see java.util.Iterator#remove() */ public void remove() { if (current == null) { throw new IllegalStateException(); } if (modCount != expectedModCount) { throw new ConcurrentModificationException(); } int k = current.key; current = null; IntHashMap.this.removeEntryForKey(k); expectedModCount = modCount; } } private class ValueIterator extends HashIterator { /** * @see java.util.Iterator#next() */ public Object next() { return nextEntry().value; } } private class KeyIterator extends HashIterator { /** * @see java.util.Iterator#next() */ public Object next() { return new Integer(nextEntry().getKey()); } } private class EntryIterator extends HashIterator { /** * @see java.util.Iterator#next() */ public Object next() { return nextEntry(); } } // Subclass overrides these to alter behavior of views' iterator() method Iterator newKeyIterator() { return new KeyIterator(); } Iterator newValueIterator() { return new ValueIterator(); } Iterator newEntryIterator() { return new EntryIterator(); } // Views private transient Set entrySet = null; /** * Returns a set view of the keys contained in this map. The set is backed * by the map, so changes to the map are reflected in the set, and * vice-versa. The set supports element removal, which removes the * corresponding mapping from this map, via the <tt>Iterator.remove</tt>, * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt>, and * <tt>clear</tt> operations. It does not support the <tt>add</tt> or * <tt>addAll</tt> operations. * * @return a set view of the keys contained in this map. */ public Set keySet() { Set ks = keySet; return (ks != null ? ks : (keySet = new KeySet())); } private class KeySet extends AbstractSet { /** * @see java.util.AbstractCollection#iterator() */ public Iterator iterator() { return newKeyIterator(); } /** * @see java.util.AbstractCollection#size() */ public int size() { return size; } /** * @see java.util.AbstractCollection#contains(java.lang.Object) */ public boolean contains(Object o) { if (o instanceof Number) { return containsKey(((Number) o).intValue()); } return false; } /** * @see java.util.AbstractCollection#remove(java.lang.Object) */ public boolean remove(Object o) { if (o instanceof Number) { return IntHashMap.this.removeEntryForKey(((Number) o).intValue()) != null; } return false; } /** * @see java.util.AbstractCollection#clear() */ public void clear() { IntHashMap.this.clear(); } } /** * Returns a collection view of the values contained in this map. The * collection is backed by the map, so changes to the map are reflected in * the collection, and vice-versa. The collection supports element removal, * which removes the corresponding mapping from this map, via the * <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>, * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> * operations. It does not support the <tt>add</tt> or <tt>addAll</tt> * operations. * * @return a collection view of the values contained in this map. */ public Collection values() { Collection vs = values; return (vs != null ? vs : (values = new Values())); } private class Values extends AbstractCollection { /** * @see java.util.AbstractCollection#iterator() */ public Iterator iterator() { return newValueIterator(); } /** * @see java.util.AbstractCollection#size() */ public int size() { return size; } /** * @see java.util.AbstractCollection#contains(java.lang.Object) */ public boolean contains(Object o) { return containsValue(o); } /** * @see java.util.AbstractCollection#clear() */ public void clear() { IntHashMap.this.clear(); } } /** * Returns a collection view of the mappings contained in this map. Each * element in the returned collection is a <tt>Map.Entry</tt>. The * collection is backed by the map, so changes to the map are reflected in * the collection, and vice-versa. The collection supports element removal, * which removes the corresponding mapping from the map, via the * <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>, * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> * operations. It does not support the <tt>add</tt> or <tt>addAll</tt> * operations. * * @return a collection view of the mappings contained in this map. * @see Map.Entry */ public Set entrySet() { Set es = entrySet; return (es != null ? es : (entrySet = new EntrySet())); } private class EntrySet extends AbstractSet { /** * @see java.util.AbstractCollection#iterator() */ public Iterator iterator() { return newEntryIterator(); } /** * @see java.util.AbstractCollection#contains(java.lang.Object) */ public boolean contains(Object o) { if (!(o instanceof Entry)) { return false; } Entry e = (Entry) o; Entry candidate = getEntry(e.getKey()); return candidate != null && candidate.equals(e); } /** * @see java.util.AbstractCollection#remove(java.lang.Object) */ public boolean remove(Object o) { return removeMapping(o) != null; } /** * @see java.util.AbstractCollection#size() */ public int size() { return size; } /** * @see java.util.AbstractCollection#clear() */ public void clear() { IntHashMap.this.clear(); } } /** * Save the state of the <tt>HashMap</tt> instance to a stream (i.e., * serialize it). * * @param s * The ObjectOutputStream * @throws IOException * * @serialData The <i>capacity</i> of the HashMap (the length of the bucket * array) is emitted (int), followed by the <i>size</i> of the * HashMap (the number of key-value mappings), followed by the * key (Object) and value (Object) for each key-value mapping * represented by the HashMap The key-value mappings are emitted * in the order that they are returned by * <tt>entrySet().iterator()</tt>. * */ private void writeObject(java.io.ObjectOutputStream s) throws IOException { // Write out the threshold, loadfactor, and any hidden stuff s.defaultWriteObject(); // Write out number of buckets s.writeInt(table.length); // Write out size (number of Mappings) s.writeInt(size); // Write out keys and values (alternating) for (Iterator i = entrySet().iterator(); i.hasNext();) { Entry e = (Entry) i.next(); s.writeInt(e.getKey()); s.writeObject(e.getValue()); } } private static final long serialVersionUID = 362498820763181265L; /** * Reconstitute the <tt>HashMap</tt> instance from a stream (i.e., * deserialize it). * * @param s * @throws IOException * @throws ClassNotFoundException */ private void readObject(java.io.ObjectInputStream s) throws IOException, ClassNotFoundException { // Read in the threshold, loadfactor, and any hidden stuff s.defaultReadObject(); // Read in number of buckets and allocate the bucket array; int numBuckets = s.readInt(); table = new Entry[numBuckets]; init(); // Give subclass a chance to do its thing. // Read in size (number of Mappings) int size = s.readInt(); // Read the keys and values, and put the mappings in the HashMap for (int i = 0; i < size; i++) { int key = s.readInt(); Object value = s.readObject(); putForCreate(key, value); } } // These methods are used when serializing HashSets int capacity() { return table.length; } float loadFactor() { return loadFactor; } }