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


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>ConstantExpression</code> represents a constant expression.</p>
19   *
20   * <p> In other words, {@link #evaluate} returns a value independent of the context. </p>
21   *
22   * @author <a HREF="mailto:jstrachan@apache.org">James Strachan</a>
23   * @version $Revision: 1.6 $
24   */
25 public class ConstantExpression implements Expression {
26
27     /** The value of this expression */
28     private Object JavaDoc value;
29     
30     /** Base constructor
31      */
32     public ConstantExpression() {
33     }
34     
35     /**
36       * Convenience constructor sets <code>value</code> property.
37       * @param value the Object which is the constant value for this expression
38       */
39     public ConstantExpression(Object JavaDoc value) {
40         this.value = value;
41     }
42     
43     /**
44       * Evaluate expression against given context.
45       *
46       * @param context evaluate expression against this context
47       * @return current value of <code>value</code> property
48       */
49     public Object JavaDoc evaluate(Context context) {
50         return value;
51     }
52     
53     /**
54      * Do nothing
55      * @see org.apache.commons.betwixt.expression.Expression
56      */
57     public void update(Context context, String JavaDoc newValue) {
58         // do nothing
59 }
60
61     /**
62      * Gets the constant value of this expression
63      * @return this expression's constant value
64      */
65     public Object JavaDoc getValue() {
66         return value;
67     }
68     
69     /**
70      * Sets the constant value of this expression
71      * @param value the constant value for this expression
72      */
73     public void setValue(Object JavaDoc value) {
74         this.value = value;
75     }
76     
77     /**
78      * Returns something useful for logging
79      * @return something useful for logging
80      */
81     public String JavaDoc toString() {
82         return "ConstantExpression [value=" + value + "]";
83     }
84 }
85
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