A major problem with marker interfaces is that an interface defines a contract for implementing classes, and that contract is inherited by all subclasses. This means that you cannot "unimplement" a marker. In the example given, if you create a subclass that you do not want to serialize (perhaps because it depends on transient state), you must resort to explicitly throwing <code>NotSerializableException</code> (per <code>ObjectOutputStream</code> docs).inhe
A better solution is for the language to support [[metadata]] directly:
* Both the [[.NET Framework|.NET framework]] and [[Java (software platform)|Java]] (as of Java 5 (1.5)) provide support for such metadata. In .NET, they are called ''"custom attributes"'', in Java they are called ''"annotations"''. Despite the different name, they are conceptually the same thing. They can be defined on classes, member variables, methods, and method parameters and may be accessed using [[Reflection_(computer_science)|reflection]].
* In [[Python (programming language)|Python]], the term "marker interface" is common in [[Zope]] and [[Plone (software)|Plone]]. Interfaces are declared as metadata and subclasses can use <code>implementsOnly</code> to declare they do not implement everything from their super classes.
