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RDF2go is an implementation-independent Java API with the design goals: portability (hence the name), performance and ease of implementation. This project was started at FZI Forschungszentrum Informatik Karlsruhe, Germany - www.fzi.de

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/**
 * LICENSE INFORMATION
 * 
 * Copyright 2005-2008 by FZI (http://www.fzi.de). Licensed under a BSD license
 * (http://www.opensource.org/licenses/bsd-license.php)  = Max Völkel
 *  = FZI Forschungszentrum Informatik Karlsruhe, Karlsruhe,
 * Germany  = 2010
 * 
 * Further project information at http://semanticweb.org/wiki/RDF2Go
 */

package org.ontoware.rdf2go.model.node;

import java.io.Serializable;


/**
 * This variable models wild-cards in triple pattern queries. Only onw instance
 * of this class if allowed: ANY. This allows type-safe methods.
 * 
 * @author voelkel
 */
public class Variable implements ResourceOrVariable, UriOrVariable, NodeOrVariable, Serializable {
	
	private static final long serialVersionUID = -2390360108847553396L;
	
	private Variable() {
	}
	
	public static final Variable ANY = new Variable();
	
	public Resource asResource() throws ClassCastException {
		throw new ClassCastException("A Variable cannot be seen as this");
	}
	
	public Literal asLiteral() throws ClassCastException {
		throw new ClassCastException("A Variable cannot be seen as this");
	}
	
	public DatatypeLiteral asDatatypeLiteral() throws ClassCastException {
		throw new ClassCastException("A Variable cannot be seen as this");
	}
	
	public LanguageTagLiteral asLanguageTagLiteral() throws ClassCastException {
		throw new ClassCastException("A Variable cannot be seen as this");
	}
	
	public URI asURI() throws ClassCastException {
		throw new ClassCastException("A Variable cannot be seen as this");
	}
	
	public BlankNode asBlankNode() throws ClassCastException {
		throw new ClassCastException("A Variable cannot be seen as this");
	}
	
	@Override
	public int hashCode() {
		return 0;
	}
	
	/**
	 * There is only one Variable, so it's equals to itself.
	 */
	@Override
	public boolean equals(Object other) {
		if(other instanceof Variable)
			return true;
		else
			return false;
	}
	
	public int compareTo(Node other) {
		if(other instanceof Variable) {
			return this.hashCode() - ((Variable)other).hashCode();
		} else {
			return 1;
		}
	}
	
	public String toSPARQL() {
		throw new RuntimeException("Variable (Singleton) can not be used for SPARQL queries");
	}
	
	/* Always returns '*' */
	@Override
	public String toString() {
		return "*";
	}
	
}