Question

I have a sample interface

 public interface SampleVariables {
int var1=0;
int var2=0;
}

and I want to use var1 and var2 across multiple classes i am trying to do this using

public class InterfaceImplementor  extends Message  implements SampleVariables{

private int var3;

public int getVar1(){
    return var1;
}

public void setVar1(int var1){
    SampleVariables.var1=var1; // ** error here in eclipse which says " remove final modifier of 'var1' " Though I have not defined it as final
}

public int getVar3() {
    return var3;
}

public void setVar3(int var3) {
    this.var3 = var3;
}

}

where class Message is a pre-defined class which I try to use and I cannot define var1, var2 in the class Message.

Is there a better way to do this? Or am I missing something really simple ?

Answer 1

All fields in an interface are implicitly static and final, hence your warning above. See this SO question for more details.

It seems to me that you want a base class with these variables, but as you’ve noted you can’t do this since you’re deriving from a 3rd party class.

I would not derive from that 3rd-party class, since you don’t control its implementation. I would rather create a class that wraps it and provides your additional functionality. That gives you a level of comfort that if/when that 3rd-party class changes, you can limit the scope of the changes that you have to subsequently make.

Unfortunately Java doesn’t support mixins, which is what you’re trying to achieve here.