/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.jena.sparql.engine.iterator;
import org.apache.jena.sparql.ARQInternalErrorException ;
import org.apache.jena.sparql.engine.ExecutionContext ;
import org.apache.jena.sparql.engine.QueryIterator ;
import org.apache.jena.sparql.engine.binding.Binding ;
public class QueryIterPeek extends QueryIter1
{
private Binding binding = null ;
private boolean closed = false ;
public static QueryIterPeek create(QueryIterator iterator, ExecutionContext cxt)
{
if ( iterator instanceof QueryIterPeek)
return (QueryIterPeek)iterator ;
return new QueryIterPeek(iterator, cxt) ;
}
private QueryIterPeek(QueryIterator iterator, ExecutionContext cxt)
{
super(iterator, cxt) ;
}
/** Returns the next binding without moving on. Returns "null" for no such element. */
public Binding peek()
{
if ( closed ) return null ;
if ( ! hasNextBinding() )
return null ;
return binding ;
}
@Override
protected boolean hasNextBinding()
{
if ( binding != null )
return true ;
if ( ! getInput().hasNext() )
return false ;
binding = getInput().nextBinding() ;
return true ;
}
@Override
protected Binding moveToNextBinding()
{
if ( ! hasNextBinding() )
throw new ARQInternalErrorException("No next binding") ;
Binding b = binding ;
binding = null ;
return b ;
}
@Override
protected void closeSubIterator()
{ closed = true ; }
@Override
protected void requestSubCancel()
{ }
}