Interfaces are mostly excluded from code coverage results, except when they are not. Non-primitive constants cause the interface to be included with 0% coverage and a red bar on the constants.
Example:
Try running "C" with coverage enabled.
public interface I {
// good
void f();
int i = 42;
float f = 42.0f;
String s2 = "Test";
// bad
Character c = new Character('c');
String s1 = new String("Test");
}
public class C implements I {
public void f() {
}
public static void main(final String[] args) {
final C c = new C();
c.f();
System.out.println(I.c);
System.out.println(I.s2);
}
}