Solution to extend multiple classes

Question

Let's say I have Class A and B that differ except on using color variables. Both classes already extend the JPanel Class so I cannot extend a new class with the color variables in it. I then thought I could make class C (with the colors in it) an interface. But it's not allowed to have attributes in an interface.

Any idea how I can still use the colors in an external class for both Class A + B?

The thought:

Class A - Uses the colors
Class B - Uses the colors
Class C - Has the colors.

define the colors in C and make a getColor method in c which returns the colors — LoremIpsum, Jun 19 '13 at 14:25
You can have a class `Z` that extends from `JPanel` and only adds a `C cHasTheColors` field, then classes `A` and `B` can extend from `Z` having all the power of `JPanel` and the `C` field in them (of course, if this is want you wanted to have). — Luiggi Mendoza, Jun 19 '13 at 14:35
What if you make the classes A and B generic? At runtime, you pass them the color you want to. — Dimitri, Jun 19 '13 at 14:40

score 0 · Answer 1 · edited May 23 '17 at 12:05

0

public interface C {
  public static final Color c1 = Color.RED;
  public static final Color c2 = Color.GREEN;
  public static final Color c3 = Color.BLUE;
}

public class A extends JPanel implements C {
    /* ... */
}

public class B extends JPanel implements C {
    /* ... */
}

EDIT: As noted in Luiggi Mendoza's comment, your Colors would have to be static and final.

edited May 23 '17 at 12:05

Community

1
1

answered Jun 19 '13 at 14:23

Dan O

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Note that fields in an interface would be marked as `static final` thus not being *shared* among the instances of the classes that implement the interface. – Luiggi Mendoza Jun 19 '13 at 14:24
So it's allowed to have static final variables in an interface? :D – Kraishan Jun 19 '13 at 15:10

score 0 · Accepted Answer · answered Jun 19 '13 at 14:23

0

You can always use an interface for storing constants.

public interface C{
    Color a;
    Color b; 
    //And so on
}

Now have A and B implement this class, and that should do it.

answered Jun 19 '13 at 14:23

JavaNewbie_M107

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Are you sure that is allowed? Please tell me if I am wrong but I was told you can only use unimplemented methods in an interface. – Kraishan Jun 19 '13 at 14:36
Well, those are `public static final` variables, not methods. I suppose that's what you wanted. – JavaNewbie_M107 Jun 19 '13 at 14:37

Solution to extend multiple classes

2 Answers2