public interface I {

public static final int a = 100;
}

public class C1 implements I {

public static final int a = 200;

}

public class C2 implements I {

public static void main(String[] args) {
System.out.println(C1.a);
System.out.println(C2.a);
}
}

実行結果
200
100

これでええんかな?