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Java > Open Source Codes > org > apache > commons > betwixt > expression > EmptyExpression


1 /*
2  * Copyright 2001-2004 The Apache Software Foundation.
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 package org.apache.commons.betwixt.expression;
17
18 /** <p><code>EmptyExpression</code> returns the same value as is passed in. </p>
19   *
20   * <p> See {@link #evaluate}. </p>
21   *
22   * @author <a HREF="mailto:jstrachan@apache.org">James Strachan</a>
23   * @version $Revision: 1.6 $
24   */
25 public class EmptyExpression implements Expression {
26     
27     /** Don't need more than one <code>EmptyExpression</code>*/
28     private static final EmptyExpression singleton = new EmptyExpression();
29     
30     /**
31      * Gets the singleton instance.
32      * @return the EmptyExpression singleton.
33      */
34     public static EmptyExpression getInstance() {
35         return singleton;
36     }
37     
38     /** Should this be private?
39      */
40     public EmptyExpression() {
41     }
42     
43     /** Return the bean we're evaluating.
44      * @see org.apache.commons.betwixt.expression.Expression
45      */
46     public Object JavaDoc evaluate(Context context) {
47         return context.getBean();
48     }
49     
50     /** Do nothing
51      * @see org.apache.commons.betwixt.expression.Expression
52      */
53     public void update(Context context, String JavaDoc newValue) {
54         // do nothing
55 }
56     
57     /**
58      * Return something useful for logging.
59      * @return short name for this class
60      */
61     public String JavaDoc toString() {
62         return "EmptyExpression";
63     }
64     
65 }
66
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