01: /*
02: * Copyright (c) 2004 JETA Software, Inc. All rights reserved.
03: *
04: * Redistribution and use in source and binary forms, with or without modification,
05: * are permitted provided that the following conditions are met:
06: *
07: * o Redistributions of source code must retain the above copyright notice,
08: * this list of conditions and the following disclaimer.
09: *
10: * o Redistributions in binary form must reproduce the above copyright notice,
11: * this list of conditions and the following disclaimer in the documentation
12: * and/or other materials provided with the distribution.
13: *
14: * o Neither the name of JETA Software nor the names of its contributors may
15: * be used to endorse or promote products derived from this software without
16: * specific prior written permission.
17: *
18: * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
19: * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20: * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
21: * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
22: * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
23: * INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
24: * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
25: * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
26: * INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
27: * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28: */
29:
30: package com.jeta.open.support;
31:
32: import java.util.AbstractCollection;
33: import java.util.Collection;
34: import java.util.Iterator;
35: import java.util.NoSuchElementException;
36:
37: /**
38: * This class is used to implement an unmodifiable collection. Any caller can
39: * get an instance of this collection (a singleton) when they need to return an
40: * empty unmodifiable collection.
41: *
42: * @author Jeff Tassin
43: */
44: public class EmptyCollection extends AbstractCollection {
45: private static EmptyCollection m_singleton = new EmptyCollection();
46: private static EmptyIterator m_iterator = new EmptyIterator();
47:
48: private EmptyCollection() {
49: // no op
50: }
51:
52: public static Collection getInstance() {
53: return m_singleton;
54: }
55:
56: public Iterator iterator() {
57: return m_iterator;
58: }
59:
60: public int size() {
61: return 0;
62: }
63:
64: private static class EmptyIterator implements Iterator {
65: public boolean hasNext() {
66: return false;
67: }
68:
69: public Object next() {
70: throw new NoSuchElementException();
71: }
72:
73: public void remove() {
74: // no op
75: }
76: }
77: }
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