001    /*
002     * Copyright 2001-2004 The Apache Software Foundation
003     *
004     * Licensed under the Apache License, Version 2.0 (the "License");
005     * you may not use this file except in compliance with the License.
006     * You may obtain a copy of the License at
007     *
008     *     http://www.apache.org/licenses/LICENSE-2.0
009     *
010     * Unless required by applicable law or agreed to in writing, software
011     * distributed under the License is distributed on an "AS IS" BASIS,
012     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013     * See the License for the specific language governing permissions and
014     * limitations under the License.
015     */
016    package org.apache.commons.cache.adt;
017    
018    /**
019     * An base implementation of {@link Listable}, supporting
020     * singly-linked lists.
021     *
022     * @version $Id: ListableBase.java 155435 2005-02-26 13:17:27Z dirkv $
023     * @author Rodney Waldhoff
024     */
025    public class ListableBase implements Listable, Cloneable {
026    
027      /** My following sibling. */
028      protected transient Listable _next = null;
029    
030      /**
031       * No arg constructor.
032       * Equivalent to {@link #ListableBase(org.apache.commons.cache.adt.Listable) <tt>ListableBase(null)</tt>}.
033       */
034      public ListableBase() {
035      }
036    
037      /**
038       * Constructor.
039       * @param next the next element in the list.
040       */
041      public ListableBase(Listable next) {
042        _next = next;
043      }
044    
045      public Listable getNext() {
046        return _next;
047      }
048    
049      public boolean hasNext() {
050        return (null != _next);
051      }
052    
053      public void setNext(Listable next) {
054        _next = next;
055      }
056    
057      /**
058       * Throws {@link UnsupportedOperationException}.
059       */
060      public Listable getPrev() throws UnsupportedOperationException {
061        throw new UnsupportedOperationException();
062      }
063    
064      /**
065       * Throws {@link UnsupportedOperationException}.
066       */
067      public boolean hasPrev() throws UnsupportedOperationException {
068        throw new UnsupportedOperationException();
069      }
070    
071      /**
072       * Throws {@link UnsupportedOperationException}.
073       */
074      public void setPrev(Listable prev) throws UnsupportedOperationException {
075        throw new UnsupportedOperationException();
076      }
077    }