接口中的Java静态方法/字段（再次！）

Question

my problem is:

• I have a bunch of different classes all extending a base class ( Identifiable ).
• I need to assign to some of the sub-class a certain value ( securityLevel ) which should be changeable and assigned to all member of the class (ie: it should be static ).
• I need to access the classes via the common ancestor.
• How do I do this?

The first thing which came to mind is to have a dedicated interface ( ISecurity ) defining either the values or a static method to access them and let the actual classes either not to implements it and, if they do, to override the static field (or method to retrieve it). However this is not possible for two reasons:

1. The current Java language does not allow static members in interface s.
2. Even if it would allow it it would not be possible to @Override it.

How can I code around the problem? The only way I found is:

• add a non- static member ( public Class getValueProvider() ) to base class to retrieve the value returning null .
• in the interested classes @Override the non- static method returning the value of a private static Class getValueProvider() implementing setters and getters for the wanted value.
• use the retrieved class instance to obtain the requested value (or skip everything if the return is null).

This is very ugly and there's no way to enforce the correct implementation in sub-classes.

Answer 1

You could define Identifiable to be an abstract class . Additionally, you can define another abstract class that extends Identifiable and adheres to your restrictions, ie holds the static variable and whatever methods may be necessary.

Answer 2

I would try to avoid any static members. Static members in java are always clamsy (you cannot override just hide them, etc.)

I'm not sure if I understand your problem corret but I suggest you construct the objects with a context interface or something. The objects then cann access these context interface if they area allowed to return a value or have to return a special value.

The one creating all these objects can pass the same object and so control the behaviour. This object could then be held static (like a singelton)

Answer 3

You could try a service/factory type of implementation. Or have some sort of class object that stores security ( SecuritySettings ) and send in the current Identifiable object to get security level

    public class Identifiable { }
    public class SampleUser extends Identifiable { }
    public class ExampleUser extends Identifiable { }

    public class UserService
    {
        public int SampleUserSecurity = 0;
        //Or an array/dictionary structure

        public int GetSecurityLevel(Identifiable user)
        {
            if(user instanceof SampleUser)
            {
                return SampleUserSecurity;
            }
        }

        public SampleUser CreateSampleUser()
        {
            return new SampleUser();
        }

        public ExampleUser CreateExampleUser()
        {
            return new ExampleUser();
        }
    }