Fields in an interface

Question

The fields in an interface must be static and final and can't be blank.
If I have for instance an interface SecurityConstraint that would have the fields name and type.
For that interface there will be various classes implementing it, and for each of those classes these fields mentioned will be different.
Now my question: is there a possibility to keep those fields in the interface since they are common for all implementing classes; or is there no other way than defining them in each of the implementing classes if they will have different values in different classes?
Thanks

Answer 1

only static constant fields should/can be defined in interfaces (and many developers myself included don't even believe constants should be declared in interfaces- that no fields should be declared in an interface.. ..but that's a separate issue). Any way, if you have a certain interface that declare security functionality, I would suggest you keep it's method structure but put all of the field declarations into into an abstract class that implements the interface, e.g.
public interface MySecurityFormat {
  public String getUserName();
//have your implementing class extend this
//class to inherit fields
public abstract class MyAbstractSecurityFormat {
  protected String userName;
  public String getUserName() {
    return userName;
}