KickJava   Java API By Example, From Geeks To Geeks.

Java > Open Source Codes > net > sf > jga > util > SingletonIterator


1 // ============================================================================
2
// $Id: SingletonIterator.java,v 1.9 2005/08/02 23:45:22 davidahall Exp $
3
// Copyright (c) 2003-2005 David A. Hall
4
// ============================================================================
5
// The contents of this file are subject to the Common Development and
6
// Distribution License (CDDL), Version 1.0 (the License); you may not use this
7
// file except in compliance with the License. You should have received a copy
8
// of the the License along with this file: if not, a copy of the License is
9
// available from Sun Microsystems, Inc.
10
//
11
// http://www.sun.com/cddl/cddl.html
12
//
13
// From time to time, the license steward (initially Sun Microsystems, Inc.) may
14
// publish revised and/or new versions of the License. You may not use,
15
// distribute, or otherwise make this file available under subsequent versions
16
// of the License.
17
//
18
// Alternatively, the contents of this file may be used under the terms of the
19
// GNU Lesser General Public License Version 2.1 or later (the "LGPL"), in which
20
// case the provisions of the LGPL are applicable instead of those above. If you
21
// wish to allow use of your version of this file only under the terms of the
22
// LGPL, and not to allow others to use your version of this file under the
23
// terms of the CDDL, indicate your decision by deleting the provisions above
24
// and replace them with the notice and other provisions required by the LGPL.
25
// If you do not delete the provisions above, a recipient may use your version
26
// of this file under the terms of either the CDDL or the LGPL.
27
//
28
// This library is distributed in the hope that it will be useful,
29
// but WITHOUT ANY WARRANTY; without even the implied warranty of
30
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
31
// ============================================================================
32
package net.sf.jga.util;
33
34 import java.util.ListIterator JavaDoc;
35 import java.util.NoSuchElementException JavaDoc;
36 import java.util.Iterator JavaDoc;
37
38 /**
39  * Iterates over a single item. The iterator is structured as a list iterator,
40  * but the list is a fixed size (1). The value may be changed after it has
41  * been retrieved at least one time.
42  *
43  * @author <a HREF="mailto:davidahall@users.sf.net">David A. Hall</a>
44  */

45
46 public class SingletonIterator<T> implements ListIterator JavaDoc<T>, Iterable JavaDoc<T> {
47     // The value returned by the iterator
48
private T _value;
49
50     // Flag indicating that the 'pointer' is set to the beginning of the
51
// imaginary list.
52
private boolean _beforeValue = true;
53
54     // Flag indicating if the current value can be changed.
55
private boolean _canSetValue = false;
56
57     /**
58      * Builds a SingletonIterator that will return the given value.
59      */

60     public SingletonIterator(T value) {
61         _value = value;
62     }
63
64     // - - - - - - - - - - -
65
// Iterable<T> interface
66
// - - - - - - - - - - -
67

68     public Iterator JavaDoc<T> iterator() { return this; }
69     
70     // - - - - - - - - - - - - -
71
// ListIterator<T> interface
72
// - - - - - - - - - - - - -
73

74     /**
75      * Returns true if the item has not yet been returned.
76      * @return true if the item has not yet been returned
77      */

78     public boolean hasNext() {
79         return _beforeValue;
80     }
81
82     /**
83      * Returns the single item
84      * @return the single item
85      * @throws NoSuchElementException if the item has already been returned
86      */

87     public T next() {
88         if (!_beforeValue)
89             throw new NoSuchElementException JavaDoc();
90
91         _beforeValue = false;
92         _canSetValue = true;
93         return _value;
94     }
95
96     /**
97      * Returns true if the item has not yet been returned.
98      * @return true if the item has not yet been returned
99      */

100     public boolean hasPrevious() {
101         return !_beforeValue;
102     }
103
104     /**
105      * Returns the single item
106      * @return the single item
107      * @throws NoSuchElementException if the item has already been returned
108      */

109     public T previous() {
110         if (_beforeValue)
111             throw new NoSuchElementException JavaDoc();
112
113         _beforeValue = true;
114         _canSetValue = true;
115         return _value;
116     }
117
118     public int nextIndex() {
119         return _beforeValue ? 0 : 1;
120     }
121
122     public int previousIndex() {
123         return _beforeValue ? -1 : 0;
124     }
125         
126     public void add(T arg)
127     {
128         throw new UnsupportedOperationException JavaDoc();
129     }
130
131     public void set(T value) {
132         if (!_canSetValue)
133             throw new IllegalStateException JavaDoc();
134
135         _value = value;
136         _canSetValue = false;
137     }
138
139     public void remove() {
140         throw new UnsupportedOperationException JavaDoc();
141     }
142 }
143
Popular Tags