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1 // Copyright 2004, 2005 The Apache Software Foundation
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // http://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14
15 package org.apache.tapestry;
16
17 import org.apache.hivemind.Locatable;
18
19 /**
20  * A binding is the mechanism used to provide values for parameters of specific {@link IComponent}
21  * instances. The component doesn't care where the required value comes from, it simply requires
22  * that a value be provided when needed.
23  * <p>
24  * Bindings are set inside the containing component's specification or template. Bindings may be
25  * invariant or dynamic (though that is irrelevant to the component). Components may also use a
26  * binding to write a value back through a property to some other object (typically, another
27  * component).
28  *
29  * @author Howard Lewis Ship
30  */
31
32 public interface IBinding extends Locatable
33 {
34     /**
35      * Returns the value of this binding. This is the essential method.
36      */
37
38     public Object JavaDoc getObject();
39
40     /**
41      * Returns the value for the binding after performing some basic checks.
42      * <p>
43      * Note: In release 4.0, the parameterName parameter was removed.
44      *
45      * @param type
46      * if not null, the value must be assignable to the specific class
47      * @throws BindingException
48      * if the value is not assignable to the specified type
49      * @since 0.2.9
50      */
51
52     public Object JavaDoc getObject(Class JavaDoc type);
53
54     /**
55      * Returns true if the value is invariant (not changing; the same value returned each time).
56      * Static and message bindings are always invariant, and
57      * {@link org.apache.tapestry.binding.ExpressionBinding}s may be marked invariant (as an
58      * optimization).
59      *
60      * @since 2.0.3
61      */
62
63     public boolean isInvariant();
64
65     /**
66      * Updates the value of the binding, if possible.
67      *
68      * @exception BindingException
69      * If the binding is read only.
70      */
71
72     public void setObject(Object JavaDoc value);
73
74     /**
75      * Returns a description of how the binding is used; this description
76      * is localized and incorporated into some exception messages.
77      *
78      * @since 4.0
79      */
80     
81     public String JavaDoc getDescription();
82 }
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