01: /*
02: * Copyright Aduna (http://www.aduna-software.com/) (c) 1997-2006.
03: *
04: * Licensed under the Aduna BSD-style license.
05: */
06: package org.openrdf.query.algebra;
07:
08: import java.util.Collections;
09: import java.util.Set;
10:
11: /**
12: * A tuple expression that contains zero solutions.
13: */
14: public class EmptySet extends QueryModelNodeBase implements TupleExpr {
15:
16: public Set<String> getBindingNames() {
17: return Collections.emptySet();
18: }
19:
20: public <X extends Exception> void visit(QueryModelVisitor<X> visitor)
21: throws X {
22: visitor.meet(this );
23: }
24:
25: @Override
26: public EmptySet clone() {
27: return (EmptySet) super.clone();
28: }
29: }
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