What is marker interface? [duplicate]

Question

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What is the use of marker interfaces in Java?

What is the use of extending marker interface.

Answer 1

A marker interface is exactly that: A means of marking that a class is or does certain things, even if those things are not expressed as actual methods. Marker interfaces date from very early on; these days while you might use one, you might also look at using annotations instead.

Answer 2

It is an interface with no methods. It is just used to "mark" Java classes which support a certain functionality like Serializable and Cloneable.