code: public static Geometry union(Geometry[] geometries,
  			SpatialReference spatialReference) {
  		OperatorUnion op = (OperatorUnion) factory
  				.getOperator(Operator.Type.Union);
  
  		SimpleGeometryCursor inputGeometries = new SimpleGeometryCursor(
  				geometries);
  		GeometryCursor result = op.execute(inputGeometries, spatialReference,
  				null);
  		return result.next();
  	}
docs: Constructs a new geometry by union an array of geometries. All inputs
  must be of the same type of geometries and share one spatial reference.
  
  See OperatorUnion.
  
  @param geometries
  The geometries to union.
  @param spatialReference
  The spatial reference of the geometries.
  @return The geometry object representing the resultant union.