Question

I have a class which holds some colors for a GUI, which the program can change to its liking. For a specific element of the GUI, I’d like to be able to specify a color which is a member of that class. In C++, I could use something like

int Pallete::*color = &Pallete::highlight;
Pallete pallete; // made in or passed to the constructor
// ...
void draw() {
    drawing.color(pallete.*color);
    // ...
}

Is there an equivalent in java? I’ve thought about using getField(String) in the Class class, or keeping the colors in a Map with string keys, but neither of these seem like very good solutions, because they rely on strings, and the compiler can’t enforce that they are actually members of Pallete. I could also put all of the color names in an enum, and have some getter function which returns the associated color, but that seems like more work for me.

Answer 1

You could just use the Integer class. Since its a class, it obeys reference semantics.

This would give you a class like

class Palette
{
    public static Integer highlight; // this gets initialize to whatever value

    public Integer color = highlight;

}

Edit

Okay, so the Integer class describes an immutable type, so you cannot change the value held by an Integer. The solution is pretty simple, though. You can just define your own, mutable class, like so:

class MyInteger {

    private int value;

    public MyInteger(int value) {
        this.value = value;
    }

    public int getValue() {
        return i;
    }

    public void setValue(int value) {
        this.value = value;
    }
}

Of course, this example only provides the most basic functionality. You could always add more if you feel like it. You may also find it useful to use an internal Integer rather than an int, or perhaps also to extend the Number class (as the Integer class does).

If you declare highlight and color to be of MyInteger type, and assign highlight to color, then changes to highlight will be reflected in color:

Palette.highlight.setValue(0);
palette.color = Palette.highlight;
Palette.highlight.setValue(1);
System.out.println(palette.color); // This line will now print "1" instead of "2"

One potential drawback of this method is that you cannot write an assignment like

Palette.highlight = 0;

Instead you must use setValue() to change the value of an instance of MyInteger. However, I don’t think this is a great loss, since it achieves the functionality you requested.