Source code: jtemporal/util/EmptySet.java
1 /*
2 Copyright (C) 2002 Thomas A Beck (http://thomas.beck.name)
3
4 This library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
8
9 This library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public
15 License along with this library; if not, write to the Free Software
16 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
17
18 package jtemporal.util;
19
20 import java.util.*;
21 import java.io.InvalidObjectException;
22 import java.io.Serializable;
23
24 /**
25 * Immutable empty read-only set (singleton). <BR>
26 * <B>For methods description, see java.util.Set</B>
27 * @author Thomas Beck
28 * @version $Id$
29 */
30 public class EmptySet extends AbstractSet implements Serializable {
31
32 private static final EmptySet INSTANCE = new EmptySet();
33 private static final long serialVersionUID = 1896628674035L;
34
35 static public EmptySet getInstance() {
36 return INSTANCE;
37 }
38
39 static final private String IMMUTABLE_ERROR = "This EmptySet is immutable";
40 static private Object[] emptyArray = new Object[0];
41
42 private EmptySet() {
43 }
44
45 /**
46 * Resolves instances being deserialized to the predefined constant.
47 */
48 private Object readResolve() throws InvalidObjectException {
49 return INSTANCE;
50 }
51
52 public boolean contains(Object o) {
53 return false;
54 }
55 public boolean remove(Object o) {
56 throw new UnsupportedOperationException(IMMUTABLE_ERROR);
57 }
58 public boolean isEmpty() {
59 return true;
60 }
61 public boolean add(Object o) {
62 throw new UnsupportedOperationException(IMMUTABLE_ERROR);
63 }
64 public int size() {
65 return 0;
66 }
67 public boolean containsAll(Collection parm1) {
68 return false;
69 }
70 public Object[] toArray() {
71 return this.emptyArray;
72 }
73 public void clear() {
74 throw new UnsupportedOperationException(IMMUTABLE_ERROR);
75 }
76 public Iterator iterator() {
77 return EmptyIterator.getInstance();
78 }
79 public boolean addAll(Collection parm1) {
80 throw new UnsupportedOperationException(IMMUTABLE_ERROR);
81 }
82 }