Java tutorial
/* * Copyright 2005 Brian S O'Neill * * 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.util.AbstractCollection; import java.util.AbstractMap; 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; import java.io.IOException; import java.io.Serializable; /** * A Map that accepts int or Integer keys only. This class is not thread-safe. * * @author Brian S O'Neill */ public class IntHashMap<V> extends AbstractMap<Integer, V> implements Map<Integer, V>, Cloneable, Serializable { /** * The hash table data. */ private transient Entry<V> table[]; /** * The total number of mappings in the hash table. */ private transient int count; /** * The table is rehashed when its size exceeds this threshold. (The * value of this field is (int)(capacity * loadFactor).) * * @serial */ private int threshold; /** * The load factor for the hashtable. * * @serial */ private float loadFactor; /** * The number of times this IntHashMap has been structurally modified * Structural modifications are those that change the number of mappings in * the IntHashMap or otherwise modify its internal structure (e.g., * rehash). This field is used to make iterators on Collection-views of * the IntHashMap fail-fast. (See ConcurrentModificationException). */ private transient int modCount = 0; /** * Constructs a new, empty map with the specified initial * capacity and the specified load factor. * * @param initialCapacity the initial capacity of the IntHashMap. * @param loadFactor the load factor of the IntHashMap * @throws IllegalArgumentException if the initial capacity is less * than zero, or if the load factor is nonpositive. */ public IntHashMap(int initialCapacity, float loadFactor) { if (initialCapacity < 0) { throw new IllegalArgumentException("Illegal Initial Capacity: " + initialCapacity); } if (loadFactor <= 0) { throw new IllegalArgumentException("Illegal Load factor: " + loadFactor); } if (initialCapacity == 0) { initialCapacity = 1; } this.loadFactor = loadFactor; table = new Entry[initialCapacity]; threshold = (int) (initialCapacity * loadFactor); } /** * Constructs a new, empty map with the specified initial capacity * and default load factor, which is <tt>0.75</tt>. * * @param initialCapacity the initial capacity of the IntHashMap. * @throws IllegalArgumentException if the initial capacity is less * than zero. */ public IntHashMap(int initialCapacity) { this(initialCapacity, 0.75f); } /** * Constructs a new, empty map with a default capacity and load * factor, which is <tt>0.75</tt>. */ public IntHashMap() { this(101, 0.75f); } /** * Constructs a new map with the same mappings as the given map. The * map is created with a capacity of twice the number of mappings in * the given map or 11 (whichever is greater), and a default load factor, * which is <tt>0.75</tt>. */ public IntHashMap(Map<? extends Integer, ? extends V> t) { this(Math.max(2 * t.size(), 11), 0.75f); putAll(t); } /** * Returns the number of key-value mappings in this map. * * @return the number of key-value mappings in this map. */ public int size() { return count; } /** * 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 count == 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) { Entry tab[] = table; if (value == null) { for (int i = tab.length; i-- > 0;) { for (Entry e = tab[i]; e != null; e = e.next) { if (e.value == null) { return true; } } } } else { for (int i = tab.length; i-- > 0;) { for (Entry e = tab[i]; e != null; e = e.next) { if (value.equals(e.value)) { return true; } } } } return false; } /** * Returns <tt>true</tt> if this map contains a mapping for the specified * key. * * @return <tt>true</tt> if this map contains a mapping for the specified * key. * @param key key whose presence in this Map is to be tested. */ public boolean containsKey(Integer key) { return containsKey(key.intValue()); } /** * Returns <tt>true</tt> if this map contains a mapping for the specified * key. * * @return <tt>true</tt> if this map contains a mapping for the specified * key. * @param key key whose presence in this Map is to be tested. */ public boolean containsKey(int key) { Entry tab[] = table; int index = (key & 0x7fffffff) % tab.length; for (Entry e = tab[index]; e != null; e = e.next) { if (e.key == key) { return true; } } return false; } /** * Returns the value to which this map maps the specified key. Returns * <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's also possible that the map * explicitly maps the key to <tt>null</tt>. The <tt>containsKey</tt> * operation may be used to distinguish these two cases. * * @return the value to which this map maps the specified key. * @param key key whose associated value is to be returned. */ public V get(Integer key) { return get(key.intValue()); } /** * Returns the value to which this map maps the specified key. Returns * <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's also possible that the map * explicitly maps the key to <tt>null</tt>. The <tt>containsKey</tt> * operation may be used to distinguish these two cases. * * @return the value to which this map maps the specified key. * @param key key whose associated value is to be returned. */ public V get(int key) { Entry<V> tab[] = table; int index = (key & 0x7fffffff) % tab.length; for (Entry<V> e = tab[index]; e != null; e = e.next) { if (e.key == key) { return e.value; } } return null; } /** * Rehashes the contents of this map into a new <tt>IntHashMap</tt> instance * with a larger capacity. This method is called automatically when the * number of keys in this map exceeds its capacity and load factor. */ private void rehash() { int oldCapacity = table.length; Entry oldMap[] = table; int newCapacity = oldCapacity * 2 + 1; Entry<V> newMap[] = new Entry[newCapacity]; modCount++; threshold = (int) (newCapacity * loadFactor); table = newMap; for (int i = oldCapacity; i-- > 0;) { for (Entry old = oldMap[i]; old != null;) { Entry e = old; old = old.next; int index = (e.key & 0x7fffffff) % newCapacity; e.next = newMap[index]; newMap[index] = 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 IntHashMap previously associated * <tt>null</tt> with the specified key. */ public V put(Integer key, V value) { return put(key.intValue(), value); } /** * 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 IntHashMap previously associated * <tt>null</tt> with the specified key. */ public V put(int key, V value) { // Makes sure the key is not already in the IntHashMap. Entry<V> tab[] = table; int index = 0; index = (key & 0x7fffffff) % tab.length; for (Entry<V> e = tab[index]; e != null; e = e.next) { if (e.key == key) { V old = e.value; e.value = value; return old; } } modCount++; if (count >= threshold) { // Rehash the table if the threshold is exceeded rehash(); tab = table; index = (key & 0x7fffffff) % tab.length; } // Creates the new entry. Entry<V> e = new Entry<V>(key, value, tab[index]); tab[index] = e; count++; return null; } /** * 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 V remove(Integer key) { return remove(key.intValue()); } /** * 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 V remove(int key) { Entry<V> tab[] = table; int index = (key & 0x7fffffff) % tab.length; for (Entry<V> e = tab[index], prev = null; e != null; prev = e, e = e.next) { if (e.key == key) { modCount++; if (prev != null) { prev.next = e.next; } else { tab[index] = e.next; } count--; V oldValue = e.value; e.value = null; return oldValue; } } return null; } /** * Removes all mappings from this map. */ public void clear() { Entry tab[] = table; modCount++; for (int index = tab.length; --index >= 0;) { tab[index] = null; } count = 0; } /** * Returns a shallow copy of this <tt>IntHashMap</tt> instance: the keys and * values themselves are not cloned. * * @return a shallow copy of this map. */ public Object clone() { try { IntHashMap t = (IntHashMap) super.clone(); t.table = new Entry[table.length]; for (int i = table.length; i-- > 0;) { t.table[i] = (table[i] != null) ? (Entry) table[i].clone() : null; } t.keySet = null; t.entrySet = null; t.values = null; t.modCount = 0; return t; } catch (CloneNotSupportedException e) { // this shouldn't happen, since we are Cloneable throw new InternalError(); } } // Views private transient Set keySet = null; private transient Set entrySet = null; private transient Collection values = 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<Integer> keySet() { if (keySet == null) { keySet = new AbstractSet<Integer>() { public Iterator iterator() { return new IntHashIterator(KEYS); } public int size() { return count; } public boolean contains(Object o) { return containsKey(o); } public boolean remove(Object o) { return IntHashMap.this.remove(o) != null; } public void clear() { IntHashMap.this.clear(); } }; } return keySet; } /** * 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<V> values() { if (values == null) { values = new AbstractCollection<V>() { public Iterator iterator() { return (Iterator) new IntHashIterator(VALUES); } public int size() { return count; } public boolean contains(Object o) { return containsValue(o); } public void clear() { IntHashMap.this.clear(); } }; } return values; } /** * 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. */ public Set<Map.Entry<Integer, V>> entrySet() { if (entrySet == null) { entrySet = new AbstractSet<Map.Entry<Integer, V>>() { public Iterator iterator() { return (Iterator) new IntHashIterator(ENTRIES); } public boolean contains(Object o) { if (!(o instanceof Map.Entry)) { return false; } Map.Entry entry = (Map.Entry) o; Integer key = (Integer) entry.getKey(); Entry tab[] = table; int hash = (key == null ? 0 : key.hashCode()); int index = (hash & 0x7fffffff) % tab.length; for (Entry e = tab[index]; e != null; e = e.next) { if (e.key == hash && e.equals(entry)) { return true; } } return false; } public boolean remove(Object o) { if (!(o instanceof Map.Entry)) { return false; } Map.Entry entry = (Map.Entry) o; Integer key = (Integer) entry.getKey(); Entry tab[] = table; int hash = (key == null ? 0 : key.hashCode()); int index = (hash & 0x7fffffff) % tab.length; for (Entry e = tab[index], prev = null; e != null; prev = e, e = e.next) { if (e.key == hash && e.equals(entry)) { modCount++; if (prev != null) { prev.next = e.next; } else { tab[index] = e.next; } count--; e.value = null; return true; } } return false; } public int size() { return count; } public void clear() { IntHashMap.this.clear(); } }; } return entrySet; } /** * IntHashMap collision list entry. */ private static class Entry<V> implements Map.Entry<Integer, V> { int key; V value; Entry<V> next; private Integer objectKey; Entry(int key, V value, Entry<V> next) { this.key = key; this.value = value; this.next = next; } protected Object clone() { return new Entry<V>(key, value, (next == null ? null : (Entry<V>) next.clone())); } // Map.Entry Ops public Integer getKey() { return (objectKey != null) ? objectKey : (objectKey = Integer.valueOf(key)); } public V getValue() { return value; } public V setValue(V value) { V oldValue = this.value; this.value = value; return oldValue; } public boolean equals(Object o) { if (!(o instanceof Map.Entry)) { return false; } Map.Entry e = (Map.Entry) o; return (getKey().equals(e.getKey())) && (value == null ? e.getValue() == null : value.equals(e.getValue())); } public int hashCode() { return key ^ (value == null ? 0 : value.hashCode()); } public String toString() { return String.valueOf(key) + "=" + value; } } // Types of Iterators private static final int KEYS = 0; private static final int VALUES = 1; private static final int ENTRIES = 2; private class IntHashIterator implements Iterator { Entry[] table = IntHashMap.this.table; int index = table.length; Entry entry; Entry lastReturned; int type; /** * The modCount value that the iterator believes that the backing * List should have. If this expectation is violated, the iterator * has detected concurrent modification. */ private int expectedModCount = modCount; IntHashIterator(int type) { this.type = type; } public boolean hasNext() { while (entry == null && index > 0) { entry = table[--index]; } return entry != null; } public Object next() { if (modCount != expectedModCount) { throw new ConcurrentModificationException(); } while (entry == null && index > 0) { entry = table[--index]; } if (entry != null) { Entry e = lastReturned = entry; entry = e.next; return type == KEYS ? e.getKey() : (type == VALUES ? e.value : e); } throw new NoSuchElementException(); } public void remove() { if (lastReturned == null) { throw new IllegalStateException(); } if (modCount != expectedModCount) { throw new ConcurrentModificationException(); } Entry<V>[] tab = IntHashMap.this.table; int index = (lastReturned.key & 0x7fffffff) % tab.length; for (Entry e = tab[index], prev = null; e != null; prev = e, e = e.next) { if (e == lastReturned) { modCount++; expectedModCount++; if (prev == null) { tab[index] = e.next; } else { prev.next = e.next; } count--; lastReturned = null; return; } } throw new ConcurrentModificationException(); } } /** * Save the state of the <tt>IntHashMap</tt> instance to a stream (i.e., * serialize it). * * @serialData The <i>capacity</i> of the IntHashMap (the length of the * bucket array) is emitted (int), followed by the * <i>size</i> of the IntHashMap (the number of key-value * mappings), followed by the key (Object) and value (Object) * for each key-value mapping represented by the IntHashMap * The key-value mappings are emitted in no particular order. */ 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(count); // Write out keys and values (alternating) for (int index = table.length - 1; index >= 0; index--) { Entry entry = table[index]; while (entry != null) { s.writeInt(entry.key); s.writeObject(entry.value); entry = entry.next; } } } /** * Reconstitute the <tt>IntHashMap</tt> instance from a stream (i.e., * deserialize it). */ 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]; // Read in size (number of Mappings) int size = s.readInt(); // Read the keys and values, and put the mappings in the IntHashMap for (int i = 0; i < size; i++) { int key = s.readInt(); V value = (V) s.readObject(); put(key, value); } } int capacity() { return table.length; } float loadFactor() { return loadFactor; } }