/*
Copyright (C) SYSTAP, LLC DBA Blazegraph 2006-2016. All rights reserved.
Contact:
SYSTAP, LLC DBA Blazegraph
2501 Calvert ST NW #106
Washington, DC 20008
licenses@blazegraph.com
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program 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 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
*/
/*
* Created on Sep 10, 2008
*/
package com.bigdata.bop.bindingSet;
import java.io.ObjectStreamException;
import java.io.Serializable;
import java.util.Iterator;
import java.util.Map.Entry;
import com.bigdata.bop.IBindingSet;
import com.bigdata.bop.IConstant;
import com.bigdata.bop.IVariable;
import cutthecrap.utils.striterators.EmptyIterator;
/**
* An immutable empty binding set.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id$
*/
@SuppressWarnings({ "rawtypes", "unchecked" })
final public class EmptyBindingSet implements IBindingSet, Serializable {
/**
*
*/
private static final long serialVersionUID = 4270590461117389862L;
/**
* Immutable singleton.
*/
public static transient final EmptyBindingSet INSTANCE = new EmptyBindingSet();
private EmptyBindingSet() {
}
/**
* @todo Clone returns the same object, which is immutable. Since we use
* clone when binding, it might be better to return a mutable object.
*/
public EmptyBindingSet clone() {
return this;
}
public EmptyBindingSet copy(IVariable[] variablesToDrop) {
return this;
}
/** Returns the same object. */
@Override
public EmptyBindingSet copyMinusErrors(final IVariable[] variablesToDrop) {
return this;
}
/**
* @return false, always
*/
@Override
public final boolean containsErrorValues() {
return false;
}
public void clear(IVariable var) {
throw new UnsupportedOperationException();
}
public void clearAll() {
throw new UnsupportedOperationException();
}
public Iterator<Entry<IVariable, IConstant>> iterator() {
return EmptyIterator.DEFAULT;
}
public void set(IVariable var, IConstant val) {
throw new UnsupportedOperationException();
}
public boolean isEmpty() {
return true;
}
public int size() {
return 0;
}
public boolean equals(final Object t) {
if (this == t)
return true;
if (!(t instanceof IBindingSet))
return false;
final IBindingSet o = (IBindingSet) t;
if (o.size() == 0)
return true;
return false;
}
/**
* The hash code of an empty binding set is always zero.
*/
public int hashCode() {
return 0;
}
public IConstant get(IVariable var) {
if (var == null)
throw new IllegalArgumentException();
return null;
}
public boolean isBound(IVariable var) {
if (var == null)
throw new IllegalArgumentException();
return false;
}
/**
* Imposes singleton pattern during object de-serialization.
*/
private Object readResolve() throws ObjectStreamException {
return EmptyBindingSet.INSTANCE;
}
public Iterator<IVariable> vars() {
return EmptyIterator.DEFAULT;
}
// public void push(IVariable[] vars) {
// throw new UnsupportedOperationException();
// }
//
// public void pop(IVariable[] vars) {
// throw new IllegalStateException();
// }
}