1 /*
2 * Copyright 2001-2004 The Apache Software Foundation
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16 package org.apache.commons.cache.adt;
17
18 import java.util.LinkedList; // only used in JavaDoc comments, but this makes the warnings go away
19 /**
20 * A simple linked-listed inteface, supporting
21 * both singly and doubly linked lists.
22 * <p>
23 * Unlike {@link java.util.LinkedList}, this interface
24 * provides access to the list elements themselves, which
25 * may necessary for some uses.
26 *
27 * @see java.util.LinkedList
28 *
29 * @version $Id: Listable.java 155435 2005-02-26 13:17:27Z dirkv $
30 * @author Rodney Waldhoff
31 */
32 public interface Listable {
33 /**
34 * Return the <tt>Listable</tt> element following me,
35 * or <tt>null</tt> if I am the last element in the
36 * list.
37 *
38 * @return the <tt>Listable</tt> element following me,
39 * or <tt>null</tt>.
40 */
41 public abstract Listable getNext();
42
43 /**
44 * Return <tt>true</tt> if there is a <tt>Listable</tt>
45 * element following me, <tt>false</tt> otherwise.
46 *
47 * @return <tt>true</tt> if there is a <tt>Listable</tt>
48 * element following me, <tt>false</tt> otherwise.
49 */
50 public abstract boolean hasNext();
51
52 /**
53 * Change my next element to <i>next</i>.
54 * Note that this does not change the {@link #getPrev}
55 * value of <i>next</i>.
56 *
57 * @param next my new following sibling.
58 * @throws UnsupportedOperationException if I am a read-only list.
59 */
60 public abstract void setNext(Listable next) throws UnsupportedOperationException;
61
62 /**
63 * Return the <tt>Listable</tt> element preceeding me,
64 * or <tt>null</tt> if I am the last element in the
65 * list.
66 *
67 * @return the <tt>Listable</tt> element preceeding me,
68 * or <tt>null</tt>.
69 * @throws UnsupportedOperationException if I am a singly-linked list.
70 */
71 public abstract Listable getPrev() throws UnsupportedOperationException;
72
73 /**
74 * Return <tt>true</tt> if there is a <tt>Listable</tt>
75 * element preceeding me, <tt>false</tt> otherwise.
76 *
77 * @return <tt>true</tt> if there is a <tt>Listable</tt>
78 * element preceeding me, <tt>false</tt> otherwise.
79 * @throws UnsupportedOperationException if I am a singly-linked list.
80 */
81 public abstract boolean hasPrev() throws UnsupportedOperationException;
82
83 /**
84 * Change my preceeding element to <i>prev</i>.
85 * Note that this does not change the {@link #getNext}
86 * value of <i>prev</i>.
87 *
88 * @param prev my new preceeding sibling.
89 * @throws UnsupportedOperationException if I am a singly-linked or read-only list.
90 */
91 public abstract void setPrev(Listable prev) throws UnsupportedOperationException;
92 }