Package org.optaplanner.core.api.domain.variable

## Annotation Type CustomShadowVariable

-     @Target({METHOD,FIELD})
      @Retention(RUNTIME)
      public @interface CustomShadowVariable

  Specifies that a bean property (or a field) is a custom shadow of 1 or more `PlanningVariable`'s.

  It is specified on a getter of a java bean property (or a field) of a `PlanningEntity` class.

- - ### Optional Element Summary

    Optional Elements
    Modifier and Type | Optional Element | Description
    --- | --- | ---
    `PlanningVariableReference[]` | `sources` | The source variables (masters) that trigger a change to this shadow variable (slave).
    `Class<? extends VariableListener>` | `variableListenerClass` | A `VariableListener` gets notified after a source planning variable has changed.
    `PlanningVariableReference` | `variableListenerRef` | Use this when this shadow variable is updated by the `VariableListener` of another `CustomShadowVariable`.

- - ### Element Detail

    - #### variableListenerClass

          Class<? extends VariableListener> variableListenerClass

      A `VariableListener` gets notified after a source planning variable has changed. That listener changes the shadow variable (often recursively on multiple planning entities) accordingly, Those shadow variables should make the score calculation more natural to write.

      For example: VRP with time windows uses a `VariableListener` to update the arrival times of all the trailing entities when an entity is changed.

      Returns:
        never null (unless `variableListenerRef()` is not null)
      Default:
        org.optaplanner.core.api.domain.variable.CustomShadowVariable.NullVariableListener.class

  - - #### sources

          PlanningVariableReference[] sources

      The source variables (masters) that trigger a change to this shadow variable (slave).
      Returns:
        never null (unless `variableListenerRef()` is not null), at least 1
      Default:
        {}

  - - #### variableListenerRef

          PlanningVariableReference variableListenerRef

      Use this when this shadow variable is updated by the `VariableListener` of another `CustomShadowVariable`.
      Returns:
        null if (and only if) any of the other fields is non null.
      Default:
        @org.optaplanner.core.api.domain.variable.PlanningVariableReference(variableName="")