Confusion in marker interface

Question

Marker interface means interface which have no methods. Then why we call the Runnable interface as a marker interface, even though it has run() method. And one more thing how many marker interfaces are there in java ?

Answer 1

Runnable is not a Marker interface. AFAIK, Serializable, Clonable, SingleThreadModel, EventListener, RandomAccess, Remote are Marker Interfaces.

Answer 2

Then why we call the Runnable interface as a marker interface

We don't. You just made that up.