Reports interface methods that clash with the protected methods clone() and finalize() in java.lang.Object. In an interface it is possible to declare those methods with a return type that is incompatible with the java.lang.Object methods. This makes it impossible to create a class implementing such an interface. When the interface is functional it remains possible to create a lambda from it, but this can still be confusing.

Example:

// Warning: this interface cannot be implemented by any class,
// only by lambda or method reference
interface MyInterface {
  double clone();
}
New in 2016.1