An interface should not have attributes.

[Luro02]

An interface

• should not have attributes/constants
• if it has attributes, those should be final and static (they are implicitly). If this is the case, one should suggest using a method with a default impl on the interface or use an enum/class
• should have methods (some use interfaces as a constant class), this should trigger the constant class lint:

interface MyConstants {
    final static String MY_CONSTANT = "Hello World";
    final static String MY_ERROR = "Input is wrong";
}

• Interfaces should be implemented by at least one class (easy indicator to detect that something is wrong with an interface)