Using Enum in java to store a fixed set of mutable objects

Question

I already posted this on Stack Overflow, but someone suggested to post it to Code Review instead.

I am creating an Android app that draws to the canvas. For this, I have defined rectangular screenareas that I want to draw to the canvas. As I am always drawing a fixed set of screenareas, I was thinking of using Enum (as Enum is designed for fixed sets).

Here is my enum:

public enum LayoutEnum {
    FULLSCREEN(
            new ScreenArea(
                new Rect(
                        0,
                        0,
                        MainActivity.getDevice().getWidth(),
                        MainActivity.getDevice().getHeight()),
                Attributes.BG_PAINT)),
    LOGO_AREA(
            new ScreenArea (
                    new Rect(
                            (int) (0.3 * FULLSCREEN.getScreenArea().getArea().width()),
                            (int) (0.3 * FULLSCREEN.getScreenArea().getArea().width()),
                            (int) (FULLSCREEN.getScreenArea().getArea().width() - 0.3 * FULLSCREEN.getScreenArea().getArea().width()),
                            (int) (0.7 * FULLSCREEN.getScreenArea().getArea().width())),
                    Attributes.BG_PAINT)
    );

    private ScreenArea screenArea;

    LayoutEnum(ScreenArea screenArea) {
        this.screenArea = screenArea;
    }

    public ScreenArea getScreenArea() {
        return screenArea;
    }
}

ScreenArea is a simple class that holds a Rect and a Paint and contains a draw method (and some getters and setters).

The question I have, is: is this a good approach? On one hand I am working with a fixed set of variables. On the other hand, these variables are mutable and I can change their attributes (e.g., using the getters and setters). For example, I can call FULLSCREEN.getScreenArea().getPaint().setColor(Color.BLUE)

When you look at Enum it says it is

a special data type that enables for a variable to be a set of predefined constant

So I do have a fixed set, it is predefined, but not necessarily constant.

My original approach was to define a class called Layout which contained a HashMap of Screenarea's. In that case, I was using e.g., Layout.get("fullscreen").draw(canvas) to draw the screenarea to the canvas. In this new approach I am using e.g., FULLSCREEN.getScreenArea().draw(canvas).

One of the reasons I would like to switch is to introduce a typesafe solution. Of course, it would also be possible to switch from a HashMap to an EnumMap and store the names of my screenareas in an Enum.

Hope you can point me in the right direction: a direction that not only works (the above is already working) but is also acceptable and doesn't smell.

Answer 1

Enums are meant to be immutable. I'd go with the EnumMap.