EmptyGraphPattern.java

/*
 * Copyright 2008 Fedora Commons
 *
 * Licensed 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.mulgara.sparql.parser.cst;

import java.util.List;
import java.util.Collections;


/**
 * Represents an empty pattern.  Matches everything.
 *
 * @created Feb 20, 2008
 * @author Paula Gearon
 * @copyright © 2008 <a href="http://www.fedora-commons.org/">Fedora Commons</a>
 * @licence <a href="{@docRoot}/../LICENCE.txt">Apache License, Version 2.0</a>
 */
public class EmptyGraphPattern extends BasicGraphPattern {

  /**
   * Normal constructor since this cannot be a singleton, due to filtering
   */
  public EmptyGraphPattern() {
  }

  /**
   * @see org.mulgara.sparql.parser.cst.BasicGraphPattern#getElements()
   */
  @SuppressWarnings("unchecked")
  @Override
  public List<GroupGraphPattern> getElements() {
    return (List<GroupGraphPattern>)Collections.EMPTY_LIST;
  }

  /**
   * @see org.mulgara.sparql.parser.cst.BasicGraphPattern#getImage()
   */
  @Override
  public String getImage() {
    return addPatterns(" { }");
  }

}