ValueHolder


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19  
20  package org.apache.cayenne;
21  
22  import java.io.Serializable  ;
23  
24  /**
25   * Provides a level of indirection for property value access, most often used for deferred
26   * faulting of to-one relationships. A ValueHolder abstracts how a property value is
27   * obtained (fetched from DB, etc.), thus simplifying design of an object that uses it.
28   * <p>
29   * Here is an example of a bean property implemented using ValueHolder:
30   * </p>
31   * 
32   * <pre>
33   * protected ValueHolder someProperty;
34   * 
35   * public SomeClass getSomeProperty() {
36   *     return (SomeClass) somePropertyHolder.getValue(SomeClass.class);
37   * }
38   * 
39   * public void setSomeProperty(SomeClass newValue) {
40   *     somePropertyHolder.setValue(SomeClass.class, newValue);
41   * }
42   * </pre>
43   * 
44   * @since 1.2
45   * @author Andrus Adamchik
46   */
47  public interface ValueHolder extends Serializable   {
48  
49      /**
50       * Returns an object stored by this ValueHolder.
51       */
52      Object   getValue() throws CayenneRuntimeException;
53  
54      /**
55       * Retrieves ValueHolder value without triggering fault resolution.
56       */
57      Object   getValueDirectly() throws CayenneRuntimeException;
58  
59      /**
60       * Sets an object stored by this ValueHolder.
61       * 
62       * @param value a new value of the ValueHolder.
63       * @return a previous value saved in the ValueHolder.
64       */
65      Object   setValue(Object   value) throws CayenneRuntimeException;
66  
67      /**
68       * Sets ValueHolder vaue without triggering fault resolution.
69       */
70      Object   setValueDirectly(Object   value) throws CayenneRuntimeException;
71  
72      /**
73       * Returns true if the internal value is not yet resolved.
74       */
75      boolean isFault();
76  
77      /**
78       * Turns a ValueHolder into a fault.
79       */
80      void invalidate();
81  }
82
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