1 /**
2 *
3 * Copyright 2003-2004 The Apache Software Foundation
4 *
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17
18 package org.apache.geronimo.gbean;
19
20 import java.util.Collection;
21 import java.util.Collections;
22 import java.util.Iterator;
23
24 /**
25 * A wrapper around a reference collection to simulate a 0..1 reference
26 */
27 public class SingleElementCollection {
28
29 private final Collection collection;
30
31 public SingleElementCollection(Object element) {
32 if (element == null) {
33 collection = Collections.EMPTY_SET;
34 } else {
35 collection = Collections.singleton(element);
36 }
37 }
38
39 public SingleElementCollection(Collection collection) {
40 if (collection == null) {
41 collection = Collections.EMPTY_SET;
42 }
43
44 this.collection = collection;
45 }
46
47 public Object getElement() {
48 if (collection.isEmpty()) {
49 return null;
50 }
51 if (collection.size() > 1) {
52 throw new IllegalStateException("More than one element: " + collection);
53 }
54 Iterator it = collection.iterator();
55 return it.next();
56 }
57
58 }