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Java > Open Source Codes > org > jicengine > element > VariableElement


1 package org.jicengine.element;
2
3 import org.jicengine.operation.Context;
4 import org.jicengine.expression.*;
5
6 /**
7  * <p>
8  * VariableElements are elements that both have a value and let the clients/users
9  * decide what to do with the value. The client/user of a VariableElement is typically
10  * the parent element.
11  * </p>
12  * <p>
13  * The latter aspect is an important one. A VariableElement doesn't actually know
14  * what to do with the value, it can only create the value. It is the responsibility
15  * of the client/user to use the value for something.
16  * </p>
17  * <p>
18  * VariableElements are usually used for producing parameters of various operations,
19  * like the constructor and action operation of an element.
20  * </p>
21  * <p>
22  * Copyright (C) 2004 Timo Laitinen
23  * </p>
24  *
25  * @author Timo Laitinen
26  * @created 2004-09-20
27  * @since JICE-0.10
28  */
29
30 public interface VariableElement extends Element {
31
32     /**
33      * <p>
34      * Creates and returns the value of this element.
35      * </p>
36      * <p>
37      * The client/user of this element will call this method. currently, the method
38      * is called only once. No caching of the result is needed. However, the
39      * object should be able to be executed multiple times.
40      * </p>
41      * <p>
42      * in general, the creation of the value consists of the following steps:
43      * </p>
44      *
45      * <ol>
46      * <li> the instance of the element is created first (with parameters)</li>
47      * <li> if the element has other ActionElements as children, they are executed next </li>
48      * <li> the instance is returned. </li>
49      * </ol>
50      *
51      * @param globalContext a Context where the instances marked with the 'id'-attribute
52      * are put.
53      *
54      * @param parentInstance the instance of the parent element. NOTE: null-value means
55      * that the value of the parent is not available (not yet
56      * or never), not that the instance of the parent is null!
57      *
58      * @return the value of the element. the operation can return null!
59      * (although that is not currently supported by other parts ozf the framework)
60      * @throws ElementException if any part of the execution of the action fails.
61      */
62     public Object JavaDoc getValue(Context globalContext, Object JavaDoc parentInstance) throws ElementException;
63
64    public Class JavaDoc getInstanceClass();
65 }
66
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