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introducing utility class from Justin Couch 

git-svn-id: https://svn.apache.org/repos/asf/jakarta/commons/proper/lang/trunk@137390 13f79535-47bb-0310-9956-ffa450edef68
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Alex Chaffee 2003-06-29 03:05:17 +00:00
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src/java/org/apache/commons/lang/IntHashMap.java Normal file
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/* ====================================================================
* The Apache Software License, Version 1.1
*
* Copyright (c) 2002-2003 The Apache Software Foundation. All rights
* reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. The end-user documentation included with the redistribution, if
* any, must include the following acknowlegement:
* "This product includes software developed by the
* Apache Software Foundation (http://www.apache.org/)."
* Alternately, this acknowlegement may appear in the software itself,
* if and wherever such third-party acknowlegements normally appear.
*
* 4. The names "The Jakarta Project", "Commons", and "Apache Software
* Foundation" must not be used to endorse or promote products derived
* from this software without prior written permission. For written
* permission, please contact apache@apache.org.
*
* 5. Products derived from this software may not be called "Apache"
* nor may "Apache" appear in their names without prior written
* permission of the Apache Software Foundation.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
* <http://www.apache.org/>.
*/
/**
* Note: originally released under the GNU LGPL v2.1, but rereleased by the original author under the ASF license (above).
*/
package org.apache.commons.lang;
/**
* A hash map that uses primitive ints for the key rather than objects.
* Note that this class is for internal optimization purposes only, and may
* not be supported in future releases of Jakarta Commons Lang. Utilities of
* this sort may be included in future releases of Jakarta Commons Collections.
*
* @author Justin Couch
* @author Alex Chaffee (alex@apache.org)
* @version $Revision: 1.1 $
* @see java.util.HashMap
*/
public class IntHashMap
{
/**
* The hash table data.
*/
private transient Entry table[];
/**
* The total number of entries 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;
/**
* Innerclass that acts as a datastructure to create a new entry in the
* table.
*/
private static class Entry
{
int hash;
int key;
Object value;
Entry next;
/**
* Create a new entry with the given values.
*
* @param hash The code used to hash the object with
* @param key The key used to enter this in the table
* @param value The value for this key
* @param next A reference to the next entry in the table
*/
protected Entry(int hash, int key, Object value, Entry next)
{
this.hash = hash;
this.key = key;
this.value = value;
this.next = next;
}
}
/**
* Constructs a new, empty hashtable with a default capacity and load
* factor, which is <tt>20</tt> and <tt>0.75</tt> respectively.
*/
public IntHashMap()
{
this(20, 0.75f);
}
/**
* Constructs a new, empty hashtable with the specified initial capacity
* and default load factor, which is <tt>0.75</tt>.
*
* @param initialCapacity the initial capacity of the hashtable.
* @throws IllegalArgumentException if the initial capacity is less
* than zero.
*/
public IntHashMap(int initialCapacity)
{
this(initialCapacity, 0.75f);
}
/**
* Constructs a new, empty hashtable with the specified initial
* capacity and the specified load factor.
*
* @param initialCapacity the initial capacity of the hashtable.
* @param loadFactor the load factor of the hashtable.
* @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 Capacity: " +
initialCapacity);
if (loadFactor <= 0)
throw new IllegalArgumentException("Illegal Load: " + loadFactor);
if (initialCapacity == 0)
initialCapacity = 1;
this.loadFactor = loadFactor;
table = new Entry[initialCapacity];
threshold = (int) (initialCapacity * loadFactor);
}
/**
* Returns the number of keys in this hashtable.
*
* @return the number of keys in this hashtable.
*/
public int size()
{
return count;
}
/**
* Tests if this hashtable maps no keys to values.
*
* @return <code>true</code> if this hashtable maps no keys to values;
* <code>false</code> otherwise.
*/
public boolean isEmpty()
{
return count == 0;
}
/**
* Tests if some key maps into the specified value in this hashtable.
* This operation is more expensive than the <code>containsKey</code>
* method.<p>
*
* Note that this method is identical in functionality to containsValue,
* (which is part of the Map interface in the collections framework).
*
* @param value a value to search for.
* @return <code>true</code> if and only if some key maps to the
* <code>value</code> argument in this hashtable as
* determined by the <tt>equals</tt> method;
* <code>false</code> otherwise.
* @throws NullPointerException if the value is <code>null</code>.
* @see #containsKey(int)
* @see #containsValue(Object)
* @see java.util.Map
*/
public boolean contains(Object value)
{
if (value == null)
{
throw new NullPointerException();
}
Entry tab[] = table;
for (int i = tab.length; i-- > 0;)
{
for (Entry e = tab[i]; e != null; e = e.next)
{
if (e.value.equals(value))
{
return true;
}
}
}
return false;
}
/**
* Returns true if this HashMap maps one or more keys to this value.<p>
*
* Note that this method is identical in functionality to contains
* (which predates the Map interface).
*
* @param value value whose presence in this HashMap is to be tested.
* @see java.util.Map
* @since JDK1.2
*/
public boolean containsValue(Object value)
{
return contains(value);
}
/**
* Tests if the specified object is a key in this hashtable.
*
* @param key possible key.
* @return <code>true</code> if and only if the specified object is a
* key in this hashtable, as determined by the <tt>equals</tt>
* method; <code>false</code> otherwise.
* @see #contains(Object)
*/
public boolean containsKey(int key)
{
Entry tab[] = table;
int hash = key;
int index = (hash & 0x7FFFFFFF) % tab.length;
for (Entry e = tab[index]; e != null; e = e.next)
{
if (e.hash == hash)
{
return true;
}
}
return false;
}
/**
* Returns the value to which the specified key is mapped in this map.
*
* @param key a key in the hashtable.
* @return the value to which the key is mapped in this hashtable;
* <code>null</code> if the key is not mapped to any value in
* this hashtable.
* @see #put(int, Object)
*/
public Object get(int key)
{
Entry tab[] = table;
int hash = key;
int index = (hash & 0x7FFFFFFF) % tab.length;
for (Entry e = tab[index]; e != null; e = e.next)
{
if (e.hash == hash)
{
return e.value;
}
}
return null;
}
/**
* Increases the capacity of and internally reorganizes this
* hashtable, in order to accommodate and access its entries more
* efficiently. This method is called automatically when the
* number of keys in the hashtable exceeds this hashtable's capacity
* and load factor.
*/
protected void rehash()
{
int oldCapacity = table.length;
Entry oldMap[] = table;
int newCapacity = oldCapacity * 2 + 1;
Entry newMap[] = new Entry[newCapacity];
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.hash & 0x7FFFFFFF) % newCapacity;
e.next = newMap[index];
newMap[index] = e;
}
}
}
/**
* Maps the specified <code>key</code> to the specified
* <code>value</code> in this hashtable. The key cannot be
* <code>null</code>. <p>
*
* The value can be retrieved by calling the <code>get</code> method
* with a key that is equal to the original key.
*
* @param key the hashtable key.
* @param value the value.
* @return the previous value of the specified key in this hashtable,
* or <code>null</code> if it did not have one.
* @throws NullPointerException if the key is <code>null</code>.
* @see #get(int)
*/
public Object put(int key, Object value)
{
// Makes sure the key is not already in the hashtable.
Entry tab[] = table;
int hash = key;
int index = (hash & 0x7FFFFFFF) % tab.length;
for (Entry e = tab[index]; e != null; e = e.next)
{
if (e.hash == hash)
{
Object old = e.value;
e.value = value;
return old;
}
}
if (count >= threshold)
{
// Rehash the table if the threshold is exceeded
rehash();
tab = table;
index = (hash & 0x7FFFFFFF) % tab.length;
}
// Creates the new entry.
Entry e = new Entry(hash, key, value, tab[index]);
tab[index] = e;
count++;
return null;
}
/**
* Removes the key (and its corresponding value) from this
* hashtable. This method does nothing if the key is not in the hashtable.
*
* @param key the key that needs to be removed.
* @return the value to which the key had been mapped in this hashtable,
* or <code>null</code> if the key did not have a mapping.
*/
public Object remove(int key)
{
Entry tab[] = table;
int hash = key;
int index = (hash & 0x7FFFFFFF) % tab.length;
for (Entry e = tab[index], prev = null; e != null; prev = e, e = e.next)
{
if (e.hash == hash)
{
if (prev != null)
{
prev.next = e.next;
}
else
{
tab[index] = e.next;
}
count--;
Object oldValue = e.value;
e.value = null;
return oldValue;
}
}
return null;
}
/**
* Clears this hashtable so that it contains no keys.
*/
public synchronized void clear()
{
Entry tab[] = table;
for (int index = tab.length; --index >= 0;)
tab[index] = null;
count = 0;
}
}