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ARQ is a SPARQL 1.1 query engine for Apache Jena
There is a newer version: 5.2.0
/*
 * 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.binding;

import java.util.HashMap ;
import java.util.Iterator ;
import java.util.Map ;

import org.apache.jena.atlas.logging.Log ;
import org.apache.jena.graph.Node ;
import org.apache.jena.sparql.ARQInternalErrorException ;
import org.apache.jena.sparql.core.Var ;
import org.apache.jena.sparql.util.FmtUtils ;

/** A muatable mapping from a name to a value such that we can create a tree of levels
 *  with higher (earlier levels) being shared.
 *  Looking up a name is done by looking in the current level,
 *  then trying the parent is not found. */

public class BindingHashMap extends BindingBase implements BindingMap
{
    // Bindings are often small.  Is this overkill? 
    Map map = new HashMap<>() ;
    
    /** Using BindingFactory.create is better */
    public BindingHashMap(Binding parent) { super(parent) ; }
    /** Using BindingFactory.create is better */
    public BindingHashMap() { super(BindingRoot.create()) ; } // null?

    /** Add a (name,value) */
    
    protected void add1(Var var, Node node)
    {
        if ( ! Var.isAnonVar(var) )
            map.put(var, node) ;
    }

    @Override
    protected int size1() { return map.size() ; }
    
    @Override
    protected boolean isEmpty1() { return map.isEmpty() ; }
    
    /** Iterate over all the names of variables.
     */
    @Override
    public Iterator vars1() 
    {
        // Assumes that varnames are NOT duplicated.
        Iterator iter = map.keySet().iterator() ;
        return iter ;
    }
    
    @Override
    public boolean contains1(Var var)
    {
        return map.containsKey(var) ;
    }
    
    @Override
    public Node get1(Var var)
    {
        return map.get(var) ;
    }

    /** Add a (var,value) - the node value is never null */
    @Override
    final public void add(Var var, Node node)
    { 
        if ( node == null )
        {
            Log.warn(this, "Binding.add: null value - ignored") ;
            return ;
        }
        checkAdd(var, node) ;
        add1(var, node) ;
    }

    @Override
    final public void addAll(Binding other)
    {
        BindingUtils.addAll(this, other) ;
    }
    
    private void checkAdd(Var var, Node node)
    {
        if ( ! CHECKING )
            return ;
        if ( var == null )
            throw new ARQInternalErrorException("check("+var+", "+node+"): null var" ) ;
        if ( node == null )
            throw new ARQInternalErrorException("check("+var+", "+node+"): null node value" ) ;
        if ( UNIQUE_NAMES_CHECK && contains(var) )
            throw new ARQInternalErrorException("Attempt to reassign '"+var+
                                                "' from '"+FmtUtils.stringForNode(get(var))+
                                                "' to '"+FmtUtils.stringForNode(node)+"'") ;
        // Let the implementation do a check as well.
        checkAdd1(var, node) ;
    }

    protected void checkAdd1(Var v, Node node) { }
}