Explain marker interfaces?
- The marker interface pattern is a design pattern in computer science, used with languages that provide run-time type information about objects.
- It provides a means to associate metadata with a class where the language does not have explicit support for such metadata.
- In java, it is used as interfaces with no method specified.
- A good example of use of marker interface in java is Serializable interface. A class implements this interface to indicate that its non-transient data members can be written to a byte steam or file system.
- 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 “un-implement” 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 NotSerializableException.
