Question

I’m doing some processing of images and in my work I use the package java.awt.geom. I am use the class Point. This class extends from Point2D and inherits get methods that return double. Point is meant to be an integer representation of a point.

To access the integer x and y values in Point you need to use publicly accessible variable x and y; My question is

1) Isn’t it bad practice to allow public access to an instance variable? eg. This question

2) Is there a better design of this?

Answer 1

Yes it is bad practice (at least by today’s standards), but there are a few reasons for this…

1. The super-class Point2D needs to be as generic as possible
2. Backwards-compatibility
3. Convenience

In detail…

1. The super-class Point2D is a generic object used to represent any kind of point that can be represented in a 2D space. In order to have maximum use as a generic class, the point needs to allow for the highest level of precision possible (ie a double). This is evident by the getX() and getY() methods that return doubles. By using doubles, it allows any sub-class to be compatible with these methods, as a double is the largest primitive java number type with precision, so any sub-class that uses any other primitive numerical variable will always be able to return it as a double without losing any precision.

   You can therefore think of Point as being a simplified version of Point2D, that doesn’t maintain any precision – however it must still conform to the abstract method declarations of the super-class Point2D. An int can be cast into a double directly by the JVM without losing any precision – if Point2D were something other than a double, you would lose some of the precision during the cast. (For example, you couldn’t cast it to a float, as larger int values wouldn’t be able to be directly represented as a float without chopping off some of the higher numbers)

2. The Point class was introduced in Java 1.0. To maintain backwards compatibility, access to these variables needs to be maintained, even though it may not be best practice. You’ll notice this in other early classes, such as the variable File.separator
3. Point is a class that is used in a lot of places, and itself is still a pretty generic object. It is much easier/simpler/quicker for programmers to reference an int directly then it is to cast every time you want to get the value (int)getX(). It is also quicker to process by the JVM, as it doesn’t need to convert an int to a double, and then back to an int again.

If you want a better design, you would probably be best to create additional methods for accessing the int values as ints – ie create the methods getXInt() and getYInt(), and then change the variables back to being non-public (provided you don’t need to retain backwards compatibility).