ActionElement


1   package org.jicengine.element;
2   
3   import org.jicengine.operation.Context;
4   
5   /**
6    * <p>
7    * ActionElements can execute an action on request. The request is made by
8    * the client or user of the ActionElement, which is usually the parent element.
9    * </p>
10   * <p>
11   * Typically, ActionElement modify global objects or the instance of the parent
12   * element by setting the values of some properties or by calling some methods.
13   * ActionElements might also call some static methods.
14   * </p>
15   * <p>
16   * Design-note: ActionElements don't return any value. the ActionElement-interface
17   * is otherwise similar to the ValueElement-interface. The two interfaces could
18   * have been put under a common interface, but in that case the action should
19   * have returned value. it was essential that action-elements don't return
20   * a value. a null-value could have been used for signalling "no value", but
21   * that approach works only if we don't use null-values otherwise..
22   * </p>
23   *
24   * <p>
25   * Elements with the 'action'-attribute are compiled into ActionElements. However,
26   * also elements without the attribute may end up as ActionElements.
27   * </p>
28   * <p>
29   * Copyright (C) 2004  Timo Laitinen
30   * </p>
31   * @author Timo Laitinen
32   * @created 2004-09-20
33   * @since JICE-0.10
34   *
35   */
36  
37  public interface ActionElement  extends Element {
38  
39      /**
40       * <p>
41       * Executes the action of this element. The operation doesn't return any
42       * value to its caller, although it can internally produce a value.
43       * </p>
44       * <p>
45       * The client/user of this element will call this method. currently, the method
46       * is called only once. However, the action should be able to be executed
47       * multiple times.
48       * </p>
49       * <p>
50       * in general, the execution consists of the following steps:
51       * </p>
52       *
53       * <ol>
54       *  <li> if the element has an instance, it is created first (with parameters)</li>
55       *  <li> if the element has other ActionElements as children, they are executed next </li>
56       *  <li> finally, the actual action is executed (with parameters) </li>
57       * </ol>
58       *
59       * @param globalContext a Context where the instances marked with the 'id'-attribute
60       *                      are put.
61       *
62       * @param parentInstance the instance of the parent element. NOTE: null-value means
63       *                       that the value of the parent is not available (not yet
64       *                       or never), not that the instance of the parent is null!
65       *
66       * @throws ElementException  if any part of the execution of the action fails.
67       */
68      public void execute(Context globalContext, Object   parentInstance) throws ElementException;
69  }
70
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