.. include-document:: org.gvsig.fmap.geom/reference-links
   :rest:

If we want to use an operation, it must be registered previously. If we try to execute an operation and it isn't registered by the GeometryManager_, we will get an exception.

The operation registration must be done in a class extended from the GeometryLibrary_, in the *postinitialize* method. The *registerGeometryOperation* method takes care of the registration of an operation. The operations must be registered indicating the concrete geometry type (or several geometry types) which are associated with them. For that, can be operations that only are valid in a subset of geometries.

For example, the PrintLn operation commented in the previous section can be executed by all geometry types. To do it, is necessary to register it following this steps:

.. code-block:: java

  GeometryManager geometryManager = GeometryLocator.getGeometryManager();
  geometryManager.registerOperation("PrintLn", printLn);

The *registerOperation* method accepts two parameters: the first one is the name of the operation and the second one is the object which implements the operation. In this case, we are registering the draw operation in the stardard output and it's associated to all geometries.

There's a mechanism to register operations associated with a concrete geometry types. We can create, for example, an operation *PrintLn* to write only 2-dimensional points. The operation will be the next:

.. code-block:: java

  public class printLnPoint2D extends GeometryOperation {
    public static final String NAME = "println";
    public static final int CODE = GeometryLocator.getGeometryManager().getGeometryOperationCode(NAME);

    public int getOperationIndex() {
      return CODE;
    }

    public Object invoke(Geometry geom, GeometryOperationContext ctx) throws GeometryOperationException {
      Point point = (Point)geom;
      System.out.println("Point 2D, X=" + point.getX() + " Y=" + point.getY());		
      return null;
    }
  }

This operation only works with objects of the type 2-dimensional point. For that, in the method *registerOperation* we must specify two new parameters: the type and subtype of the geometry which can use the operation. When the *PrintLn* operation is invoked, the code of the operation *PrintLn* will be executed for all the geometry types except to the 2-dimensional Point_, which will execute the specific operation. 

.. code-block:: java

  GeometryManager geometryManager = GeometryLocator.getGeometryManager();
  geometryManager.registerOperation("PrintLn", printLnPoint2D, Geometry.TYPES.Point, Geometry.SUBTYPES.GEOM2D);

The *registerOperation* method is overwritted to let us to associate an operation to all the geometry of a concrete type (for all the subtypes). This example shows how to do an operation that prints points, independently of their dimensions.

.. code-block:: java

  public class printLnPoint extends GeometryOperation {
    public static final String NAME = "println";
    public static final int CODE = GeometryLocator.getGeometryManager().getGeometryOperationCode(NAME);

    public int getOperationIndex() {
      return CODE;
    }

    public Object invoke(Geometry geom, GeometryOperationContext ctx) throws GeometryOperationException {
      Point point = (Point)geom;
      System.out.println("Point, ");
      for (int i=0 ; i
        


         

        
        

          


        

        
        

        

  

  
    

      

        

          
            
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