org.j3d.util.CharHashMap Maven / Gradle / Ivy
/*****************************************************************************
* J3D.org Copyright (c) 2001
* Java Source
*
* This source is licensed under the GNU LGPL v2.1
* Please read http://www.gnu.org/copyleft/lgpl.html for more information
*
* This software comes with the standard NO WARRANTY disclaimer for any
* purpose. Use it at your own risk. If there's a problem you get to fix it.
*
****************************************************************************/
package org.j3d.util;
/**
* A hash map that uses primitive chars for the key rather than objects.
*
*
*
* @author Justin Couch
* @version $Revision: 1.1 $
* @see java.util.HashMap
*/
public class CharHashMap
{
/**
* 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;
char key;
T 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, char key, T 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 20 and 0.75 respectively.
*/
public CharHashMap()
{
this(20, 0.75f);
}
/**
* Constructs a new, empty hashtable with the specified initial capacity
* and default load factor, which is 0.75.
*
* @param initialCapacity the initial capacity of the hashtable.
* @throws IllegalArgumentException if the initial capacity is less
* than zero.
*/
public CharHashMap(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 CharHashMap(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 true if this hashtable maps no keys to values;
* false 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 containsKey
* method.
*
* 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 true if and only if some key maps to the
* value argument in this hashtable as
* determined by the equals method;
* false otherwise.
* @throws NullPointerException if the value is null.
* @see #containsKey(char)
* @see #containsValue(Object)
* @see java.util.Map
*/
public boolean contains(V 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.
*
* 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(V value)
{
return contains(value);
}
/**
* Tests if the specified object is a key in this hashtable.
*
* @param key possible key.
* @return true if and only if the specified object is a
* key in this hashtable, as determined by the equals
* method; false otherwise.
* @see #contains(Object)
*/
public boolean containsKey(char 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;
* null if the key is not mapped to any value in
* this hashtable.
* @see #put(char, Object)
*/
public V get(char 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 key to the specified
* value in this hashtable. The key cannot be
* null.
*
* The value can be retrieved by calling the get 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 null if it did not have one.
* @throws NullPointerException if the key is null.
* @see #get(char)
*/
public Object put(char key, V 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 null if the key did not have a mapping.
*/
public Object remove(char 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;
}
}