code: public double getDoublePropertyFallback(T property) throws NumberFormatException
      {
          try
          {
              return Double.parseDouble(getProperty(property));
          }
          catch (NumberFormatException e)
          {
              return Double.parseDouble(getDefaultProperty(property));
          }
      }
docs: Retrieve the value of the given property as a double. If the current
  value of the specified property cannot be converted to a double, the
  default value will be retrieved.
  
  @param property
  the property to retrieve
  @return the double value of the given property or the default value if
  the current value is not a valid double
  @throws NumberFormatException
  if both the current and default values are not doubles