private void execute(Polygon polygon) {
   LinearRing ring = null;
   if (index.isExteriorRing()) {
     ring = polygon.getExteriorRing();
     if (ring == null) {
       ring = polygon.getGeometryFactory().createLinearRing(new Coordinate[] {coordinate});
       setExteriorRing(polygon, ring);
     } else {
       setExteriorRing(polygon, (LinearRing) execute(ring));
     }
   } else if (index.getInteriorRingIndex() >= 0) {
     if (index.getGeometryIndex() >= polygon.getNumInteriorRing()) {
       LinearRing[] interiorRings = new LinearRing[polygon.getNumInteriorRing() + 1];
       for (int i = 0; i < polygon.getNumInteriorRing(); i++) {
         interiorRings[i] = polygon.getInteriorRingN(i);
       }
       interiorRings[polygon.getNumInteriorRing()] =
           polygon.getGeometryFactory().createLinearRing(new Coordinate[] {coordinate});
       setInteriorRings(polygon, interiorRings);
     } else {
       ring = polygon.getInteriorRingN(index.getInteriorRingIndex());
       LineString lineString = execute(ring);
       setInteriorRingN(polygon, (LinearRing) lineString, index.getInteriorRingIndex());
     }
   }
 }
 @Test
 public void testLineStringMiddleIndex() {
   GeometryOperation op = new RemoveRingOperation(1);
   Polygon result = (Polygon) op.execute(polygon);
   Assert.assertEquals(polygon.getNumInteriorRing() - 1, result.getNumInteriorRing());
   Assert.assertEquals(12.0, result.getInteriorRingN(0).getCoordinate().getX(), TOLERANCE);
 }
  private void draw(
      Object parentGroup, GeometryIndex parentIndex, Polygon polygon, GraphicsContext graphics) {
    String groupName = baseName;
    if (parentIndex != null) {
      groupName += "." + editingService.getIndexService().format(parentIndex);
    }

    Composite bgGroup = getOrCreateGroup(parentGroup, groupName + ".background");
    Composite geometryGroup = getOrCreateGroup(parentGroup, groupName + ".geometries");

    // Draw the exterior ring:
    GeometryIndex shellIndex =
        editingService
            .getIndexService()
            .addChildren(parentIndex, GeometryIndexType.TYPE_GEOMETRY, 0);
    if (!polygon.isEmpty()) {
      if (styleService.getBackgroundStyle() != null
          && styleService.getBackgroundStyle().getFillOpacity() > 0) {
        graphics.drawPolygon(bgGroup, "background", polygon, findGeometryStyle(shellIndex));
      }
      draw(geometryGroup, shellIndex, polygon.getExteriorRing(), graphics);
    }

    // Draw the interior rings:
    for (int i = 0; i < polygon.getNumInteriorRing(); i++) {
      GeometryIndex holeIndex =
          editingService
              .getIndexService()
              .addChildren(parentIndex, GeometryIndexType.TYPE_GEOMETRY, i + 1);
      draw(geometryGroup, holeIndex, polygon.getInteriorRingN(i), graphics);
    }
  }