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///////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2001, Eric D. Friedman All Rights Reserved.
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
///////////////////////////////////////////////////////////////////////////////
package gnu.trove;
/**
* An open addressed hashing implementation for Object types.
*
* Created: Sun Nov 4 08:56:06 2001
*
* @author Eric D. Friedman
* @version $Id: TObjectHash.java,v 1.8 2004/09/24 09:11:15 cdr Exp $
*/
public abstract class TObjectHash extends THash implements TObjectHashingStrategy {
/** the set of Objects */
protected transient Object[] _set;
/** the strategy used to hash objects in this collection. */
protected final TObjectHashingStrategy _hashingStrategy;
public static final Object REMOVED = new Object();
private static class NULL { NULL() {}}
public static final NULL NULL = new NULL();
/**
* Creates a new TObjectHash instance with the
* default capacity and load factor.
*/
public TObjectHash() {
_hashingStrategy = this;
}
/**
* Creates a new TObjectHash instance with the
* default capacity and load factor and a custom hashing strategy.
*
* @param strategy used to compute hash codes and to compare objects.
*/
public TObjectHash(TObjectHashingStrategy strategy) {
_hashingStrategy = strategy;
}
/**
* Creates a new TObjectHash instance whose capacity
* is the next highest prime above initialCapacity + 1
* unless that value is already prime.
*
* @param initialCapacity an int value
*/
public TObjectHash(int initialCapacity) {
super(initialCapacity);
_hashingStrategy = this;
}
/**
* Creates a new TObjectHash instance whose capacity
* is the next highest prime above initialCapacity + 1
* unless that value is already prime. Uses the specified custom
* hashing strategy.
*
* @param initialCapacity an int value
* @param strategy used to compute hash codes and to compare objects.
*/
public TObjectHash(int initialCapacity, TObjectHashingStrategy strategy) {
super(initialCapacity);
_hashingStrategy = strategy;
}
/**
* Creates a new TObjectHash instance with a prime
* value at or near the specified capacity and load factor.
*
* @param initialCapacity used to find a prime capacity for the table.
* @param loadFactor used to calculate the threshold over which
* rehashing takes place.
*/
public TObjectHash(int initialCapacity, float loadFactor) {
super(initialCapacity, loadFactor);
_hashingStrategy = this;
}
/**
* Creates a new TObjectHash instance with a prime
* value at or near the specified capacity and load factor. Uses
* the specified custom hashing strategy.
*
* @param initialCapacity used to find a prime capacity for the table.
* @param loadFactor used to calculate the threshold over which
* rehashing takes place.
* @param strategy used to compute hash codes and to compare objects.
*/
public TObjectHash(int initialCapacity, float loadFactor, TObjectHashingStrategy strategy) {
super(initialCapacity, loadFactor);
_hashingStrategy = strategy;
}
/**
* @return a shallow clone of this collection
*/
@Override
public TObjectHash clone() {
TObjectHash h = (TObjectHash)super.clone();
h._set = _set == EMPTY_OBJECT_ARRAY ? EMPTY_OBJECT_ARRAY : _set.clone();
return h;
}
@Override
protected int capacity() {
return _set.length;
}
@Override
protected void removeAt(int index) {
_set[index] = REMOVED;
super.removeAt(index);
}
/**
* initializes the Object set of this hash table.
*
* @param initialCapacity an int value
* @return an int value
*/
@Override
protected int setUp(int initialCapacity) {
int capacity = super.setUp(initialCapacity);
_set = initialCapacity == JUST_CREATED_CAPACITY ? EMPTY_OBJECT_ARRAY : new Object[capacity];
return capacity;
}
/**
* Executes procedure for each element in the set.
*
* @param procedure a TObjectProcedure value
* @return false if the loop over the set terminated because
* the procedure returned false for some value.
*/
public boolean forEach(TObjectProcedure procedure) {
Object[] set = _set;
for (int i = set.length; i-- > 0;) {
if (set[i] != null
&& set[i] != REMOVED
&& ! procedure.execute((T) set[i])) {
return false;
}
}
return true;
}
/**
* Searches the set for obj
*
* @param obj an Object value
* @return a boolean value
*/
public boolean contains(Object obj) {
return index((T) obj) >= 0;
}
/**
* Locates the index of obj.
*
* @param obj an Object value
* @return the index of obj or -1 if it isn't in the set.
*/
protected int index(T obj) {
Object[] set = _set;
if (set == EMPTY_OBJECT_ARRAY) return -1;
int length = set.length;
int hash = _hashingStrategy.computeHashCode(obj) & 0x7fffffff;
int index = hash % length;
Object cur = set[index];
if (cur != null
&& (cur == REMOVED || ! _hashingStrategy.equals((T) cur, obj))) {
// see Knuth, p. 529
int probe = 1 + hash % (length - 2);
do {
index -= probe;
if (index < 0) {
index += length;
}
cur = set[index];
} while (cur != null
&& (cur == REMOVED || ! _hashingStrategy.equals((T) cur, obj)));
}
return cur == null ? -1 : index;
}
/**
* Locates the index at which obj can be inserted. if
* there is already a value equal()ing obj in the set,
* returns that value's index as -index - 1.
*
* @param obj an Object value
* @return the index of a FREE slot at which obj can be inserted
* or, if obj is already stored in the hash, the negative value of
* that index, minus 1: -index -1.
*/
protected int insertionIndex(T obj) {
if (_set == EMPTY_OBJECT_ARRAY) {
setUp((int) (DEFAULT_INITIAL_CAPACITY / DEFAULT_LOAD_FACTOR + 1));
}
Object[] set = _set;
int length = set.length;
int hash = _hashingStrategy.computeHashCode(obj) & 0x7fffffff;
int index = hash % length;
Object cur = set[index];
if (cur == null) {
return index; // empty, all done
}
if (cur != REMOVED && _hashingStrategy.equals((T) cur, obj)) {
return -index -1; // already stored
}
// already FULL or REMOVED, must probe
// compute the double hash
int probe = 1 + hash % (length - 2);
// keep track of the first removed cell. it's the natural candidate for re-insertion
int firstRemoved = cur == REMOVED ? index : -1;
// starting at the natural offset, probe until we find an
// offset that isn't full.
do {
index -= probe;
if (index < 0) {
index += length;
}
cur = set[index];
if (firstRemoved == -1 && cur == REMOVED) {
firstRemoved = index;
}
}
while (cur != null
&& cur != REMOVED
&& !_hashingStrategy.equals((T) cur, obj));
// if the index we found was removed: continue probing until we
// locate a free location or an element which equal()s the
// one we have.
if (cur == REMOVED) {
while (cur != null
&& (cur == REMOVED || !_hashingStrategy.equals((T) cur, obj))) {
index -= probe;
if (index < 0) {
index += length;
}
cur = set[index];
}
}
// if it's full, the key is already stored
if (cur != null) {
return -index -1;
}
return firstRemoved == -1 ? index : firstRemoved;
}
/**
* This is the default implementation of TObjectHashingStrategy:
* it delegates hashing to the Object's hashCode method.
*
* @param o for which the hashcode is to be computed
* @return the hashCode
* @see Object#hashCode()
*/
public final int computeHashCode(T o) {
return o != null ? o.hashCode() : 0;
}
/**
* This is the default implementation of TObjectHashingStrategy:
* it delegates equality comparisons to the first parameter's
* equals() method.
*
* @param o1 an Object value
* @param o2 an Object value
* @return true if the objects are equal
* @see Object#equals(Object)
*/
public final boolean equals(T o1, T o2) {
return o1 != null ? o1.equals(o2) : o2 == null;
}
/**
* Convenience methods for subclasses to use in throwing exceptions about
* badly behaved user objects employed as keys. We have to throw an
* IllegalArgumentException with a rather verbose message telling the
* user that they need to fix their object implementation to conform
* to the general contract for java.lang.Object.
*
* @param o1 the first of the equal elements with unequal hash codes.
* @param o2 the second of the equal elements with unequal hash codes.
* @exception IllegalArgumentException the whole point of this method.
*/
protected final void throwObjectContractViolation(Object o1, Object o2)
throws IllegalArgumentException {
throw new IllegalArgumentException("Equal objects must have equal hashcodes. "
+ "During rehashing, Trove discovered that "
+ "the following two objects claim to be "
+ "equal (as in java.lang.Object.equals() or TObjectHashingStrategy.equals()) "
+ "but their hashCodes (or those calculated by "
+ "your TObjectHashingStrategy) are not equal."
+ "This violates the general contract of "
+ "java.lang.Object.hashCode(). See bullet point two "
+ "in that method's documentation. "
+ "object #1 =" + o1 + (o1 == null ? "" : " ("+o1.getClass()+")")
+ ", hashCode="+_hashingStrategy.computeHashCode((T)o1)
+ "; object #2 =" + o2 + (o2 == null ? "" : " ("+o2.getClass()+")")
+ ", hashCode="+_hashingStrategy.computeHashCode((T)o2)
);
}
} // TObjectHash