Confusion in marker interface

Marker interface means interface which have no methods. Then why we call the Runnable interface as开发者_开发百科 a marker interface, even though it has run() method. And one more thing how many marker interfaces are there in java ?

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Then why we call the Runnable interface as a marker interface

We don't. You just made that up.

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