EmptyBindingSet.java
/*******************************************************************************
* Copyright (c) 2015 Eclipse RDF4J contributors, Aduna, and others.
*
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Distribution License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/org/documents/edl-v10.php.
*
* SPDX-License-Identifier: BSD-3-Clause
*******************************************************************************/
package org.eclipse.rdf4j.query.impl;
import java.util.Collections;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Set;
import org.eclipse.rdf4j.model.Value;
import org.eclipse.rdf4j.query.Binding;
import org.eclipse.rdf4j.query.BindingSet;
/**
* An immutable empty BindingSet.
*
* @author Arjohn Kampman
*/
public class EmptyBindingSet implements BindingSet {
private static final long serialVersionUID = -6010968140688315954L;
private static final EmptyBindingSet singleton = new EmptyBindingSet();
public static BindingSet getInstance() {
return singleton;
}
private final EmptyBindingIterator iter = new EmptyBindingIterator();
@Override
public Iterator<Binding> iterator() {
return iter;
}
@Override
public Set<String> getBindingNames() {
return Collections.emptySet();
}
@Override
public Binding getBinding(String bindingName) {
return null;
}
@Override
public boolean hasBinding(String bindingName) {
return false;
}
@Override
public Value getValue(String bindingName) {
return null;
}
@Override
public int size() {
return 0;
}
@Override
public boolean equals(Object o) {
if (o instanceof BindingSet) {
return ((BindingSet) o).isEmpty();
}
return false;
}
@Override
public int hashCode() {
return 0;
}
@Override
public String toString() {
return "[]";
}
/*----------------------------------*
* Inner class EmptyBindingIterator *
*----------------------------------*/
private static class EmptyBindingIterator implements Iterator<Binding> {
@Override
public boolean hasNext() {
return false;
}
@Override
public Binding next() {
throw new NoSuchElementException();
}
@Override
public void remove() {
throw new IllegalStateException();
}
}
}