Marker Interfaces in Java

Question

Is there a list of standard marker interfaces in Java? I've read (in some Java book) that marker interfaces do not have any methods to implement , however when I did a google search - there are certain answers which specify that marker interfaces can indeed have methods. If that is the case then I think there is no difference between a regular interface and marker interface - would it be possible to clear my confusion :)

Answer 1

There is indeed no technical difference between "standard" and "marker" interfaces.

Normally you define an interface to define methods that implementing classes should have. If you don't specify any methods you call the interface a marker interface, since if only marks the class as having some property.

Examples of that are Serializable, Cloneable etc. Those interfaces don't define any methods themselves, but by convention and specification you have to option to implement some special methods related to them, e.g. some serializaton methods related to Serializable. The core Java libraries would then use reflection to check whether those methods exist if a marker interface is implemented.

Answer 2

There is at least one: Serializable. I personally do not remember others. The technique of defining ta interfaces is old and almost obsolete since java 1.5 when annotations were introduced, so you can use annotation to "tag" class instead of empty interface.