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Java > Open Source Codes > org > apache > geronimo > gbean > SingleElementCollection


1 /**
2  * Licensed to the Apache Software Foundation (ASF) under one or more
3  * contributor license agreements. See the NOTICE file distributed with
4  * this work for additional information regarding copyright ownership.
5  * The ASF licenses this file to You under the Apache License, Version 2.0
6  * (the "License"); you may not use this file except in compliance with
7  * the License. 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 JavaDoc;
21 import java.util.Collections JavaDoc;
22 import java.util.Iterator JavaDoc;
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 JavaDoc collection;
30
31     public SingleElementCollection(Object JavaDoc element) {
32         if (element == null) {
33             collection = Collections.EMPTY_SET;
34         } else {
35             collection = Collections.singleton(element);
36         }
37     }
38
39     public SingleElementCollection(Collection JavaDoc collection) {
40         if (collection == null) {
41             collection = Collections.EMPTY_SET;
42         }
43
44         this.collection = collection;
45     }
46
47     public Object JavaDoc getElement() {
48         if (collection.isEmpty()) {
49             return null;
50         }
51         if (collection.size() > 1) {
52             throw new IllegalStateException JavaDoc("More than one element: " + collection);
53         }
54         Iterator JavaDoc it = collection.iterator();
55         return it.next();
56     }
57
58 }
59
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