Object Int Map
/* Copyright (C) 2003 Vladimir Roubtsov. All rights reserved.
*
* This program and the accompanying materials are made available under
* the terms of the Common Public License v1.0 which accompanies this distribution,
* and is available at http://www.eclipse.org/legal/cpl-v10.html
*
* $Id: ObjectIntMap.java,v 1.1.1.1 2004/05/09 16:57:54 vlad_r Exp $
*/
// ----------------------------------------------------------------------------
/**
*
* MT-safety: an instance of this class is <I>not</I> safe for access from
* multiple concurrent threads [even if access is done by a single thread at a
* time]. The caller is expected to synchronize externally on an instance [the
* implementation does not do internal synchronization for the sake of efficiency].
* java.util.ConcurrentModificationException is not supported either.
*
* @author (C) 2001, Vlad Roubtsov
*/
public
final class ObjectIntMap
{
// public: ................................................................
// TODO: optimize key comparisons using key.hash == entry.key.hash condition
/**
* Equivalent to <CODE>IntObjectMap(11, 0.75F)</CODE>.
*/
public ObjectIntMap ()
{
this (11, 0.75F);
}
/**
* Equivalent to <CODE>IntObjectMap(capacity, 0.75F)</CODE>.
*/
public ObjectIntMap (final int initialCapacity)
{
this (initialCapacity, 0.75F);
}
/**
* Constructs an IntObjectMap with specified initial capacity and load factor.
*
* @param initialCapacity initial number of hash buckets in the table [may not be negative, 0 is equivalent to 1].
* @param loadFactor the load factor to use to determine rehashing points [must be in (0.0, 1.0] range].
*/
public ObjectIntMap (int initialCapacity, final float loadFactor)
{
if (initialCapacity < 0) throw new IllegalArgumentException ("negative input: initialCapacity [" + initialCapacity + "]");
if ((loadFactor <= 0.0) || (loadFactor >= 1.0 + 1.0E-6))
throw new IllegalArgumentException ("loadFactor not in (0.0, 1.0] range: " + loadFactor);
if (initialCapacity == 0) initialCapacity = 1;
m_loadFactor = loadFactor > 1.0 ? 1.0F : loadFactor;
m_sizeThreshold = (int) (initialCapacity * loadFactor);
m_buckets = new Entry [initialCapacity];
}
/**
* Overrides Object.toString() for debug purposes.
*/
public String toString ()
{
final StringBuffer s = new StringBuffer ();
debugDump (s);
return s.toString ();
}
/**
* Returns the number of key-value mappings in this map.
*/
public int size ()
{
return m_size;
}
public boolean contains (final Object key)
{
// index into the corresponding hash bucket:
final Entry [] buckets = m_buckets;
final int keyHash = key.hashCode ();
final int bucketIndex = (keyHash & 0x7FFFFFFF) % buckets.length;
// traverse the singly-linked list of entries in the bucket:
for (Entry entry = buckets [bucketIndex]; entry != null; entry = entry.m_next)
{
if ((keyHash == entry.m_key.hashCode ()) || entry.m_key.equals (key))
return true;
}
return false;
}
/**
* Returns the value that is mapped to a given 'key'. Returns
* false if this key has never been mapped.
*
* @param key mapping key [may not be null]
* @param out holder for the found value [must be at least of size 1]
*
* @return 'true' if this key was mapped to an existing value
*/
public boolean get (final Object key, final int [] out)
{
// index into the corresponding hash bucket:
final Entry [] buckets = m_buckets;
final int keyHash = key.hashCode ();
final int bucketIndex = (keyHash & 0x7FFFFFFF) % buckets.length;
// traverse the singly-linked list of entries in the bucket:
for (Entry entry = buckets [bucketIndex]; entry != null; entry = entry.m_next)
{
if ((keyHash == entry.m_key.hashCode ()) || entry.m_key.equals (key))
{
out [0] = entry.m_value;
return true;
}
}
return false;
}
public Object [] keys ()
{
final Object [] result = new Object [m_size];
int scan = 0;
for (int b = 0; b < m_buckets.length; ++ b)
{
for (Entry entry = m_buckets [b]; entry != null; entry = entry.m_next)
{
result [scan ++] = entry.m_key;
}
}
return result;
}
/**
* Updates the table to map 'key' to 'value'. Any existing mapping is overwritten.
*
* @param key mapping key [may not be null]
* @param value mapping value.
*/
public void put (final Object key, final int value)
{
Entry currentKeyEntry = null;
// detect if 'key' is already in the table [in which case, set 'currentKeyEntry' to point to its entry]:
// index into the corresponding hash bucket:
final int keyHash = key.hashCode ();
int bucketIndex = (keyHash & 0x7FFFFFFF) % m_buckets.length;
// traverse the singly-linked list of entries in the bucket:
Entry [] buckets = m_buckets;
for (Entry entry = buckets [bucketIndex]; entry != null; entry = entry.m_next)
{
if ((keyHash == entry.m_key.hashCode ()) || entry.m_key.equals (key))
{
currentKeyEntry = entry;
break;
}
}
if (currentKeyEntry != null)
{
// replace the current value:
currentKeyEntry.m_value = value;
}
else
{
// add a new entry:
if (m_size >= m_sizeThreshold) rehash ();
buckets = m_buckets;
bucketIndex = (keyHash & 0x7FFFFFFF) % buckets.length;
final Entry bucketListHead = buckets [bucketIndex];
final Entry newEntry = new Entry (key, value, bucketListHead);
buckets [bucketIndex] = newEntry;
++ m_size;
}
}
/**
* Updates the table to map 'key' to 'value'. Any existing mapping is overwritten.
*
* @param key mapping key [may not be null]
*/
public void remove (final Object key)
{
// index into the corresponding hash bucket:
final int keyHash = key.hashCode ();
final int bucketIndex = (keyHash & 0x7FFFFFFF) % m_buckets.length;
// traverse the singly-linked list of entries in the bucket:
Entry [] buckets = m_buckets;
for (Entry entry = buckets [bucketIndex], prev = entry; entry != null; )
{
final Entry next = entry.m_next;
if ((keyHash == entry.m_key.hashCode ()) || entry.m_key.equals (key))
{
if (prev == entry)
buckets [bucketIndex] = next;
else
prev.m_next = next;
-- m_size;
break;
}
prev = entry;
entry = next;
}
}
// protected: .............................................................
// package: ...............................................................
void debugDump (final StringBuffer out)
{
if (out != null)
{
out.append (super.toString ()); out.append (EOL);
out.append ("size = " + m_size + ", bucket table size = " + m_buckets.length + ", load factor = " + m_loadFactor + EOL);
out.append ("size threshold = " + m_sizeThreshold + EOL);
}
}
// private: ...............................................................
/**
* The structure used for chaining colliding keys.
*/
private static final class Entry
{
Entry (final Object key, final int value, final Entry next)
{
m_key = key;
m_value = value;
m_next = next;
}
Object m_key; // reference to the value [never null]
int m_value;
Entry m_next; // singly-linked list link
} // end of nested class
/**
* Re-hashes the table into a new array of buckets.
*/
private void rehash ()
{
// TODO: it is possible to run this method twice, first time using the 2*k+1 prime sequencer for newBucketCount
// and then with that value reduced to actually shrink capacity. As it is right now, the bucket table can
// only grow in size
final Entry [] buckets = m_buckets;
final int newBucketCount = (m_buckets.length << 1) + 1;
final Entry [] newBuckets = new Entry [newBucketCount];
// rehash all entry chains in every bucket:
for (int b = 0; b < buckets.length; ++ b)
{
for (Entry entry = buckets [b]; entry != null; )
{
final Entry next = entry.m_next; // remember next pointer because we are going to reuse this entry
final int entryKeyHash = entry.m_key.hashCode () & 0x7FFFFFFF;
// index into the corresponding new hash bucket:
final int newBucketIndex = entryKeyHash % newBucketCount;
final Entry bucketListHead = newBuckets [newBucketIndex];
entry.m_next = bucketListHead;
newBuckets [newBucketIndex] = entry;
entry = next;
}
}
m_sizeThreshold = (int) (newBucketCount * m_loadFactor);
m_buckets = newBuckets;
}
private final float m_loadFactor; // determines the setting of m_sizeThreshold
private Entry [] m_buckets; // table of buckets
private int m_size; // number of keys in the table, not cleared as of last check
private int m_sizeThreshold; // size threshold for rehashing
private static final String EOL = System.getProperty ("line.separator", "\n");
} // end of class
// ----------------------------------------------------------------------------
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