What is marker interface in java?

Marker Interface in java does not contains any method or field or constant declared within it. Thus we can say, a marker interface is an empty interface.

Example of marker interface

• Serializable, 
• Cloneable, 
• RandomAccess interface, and 
• Remote interface

The question that immediately pops-up in our mind is:

• Why would one declare an empty interface? 
• What good is it of?

In general a common belief is that a marker interface is generally used to send some kind of signal to the JVM and instructs JVM to  treat the class implementing it in a special way.

Like, when a class implements Cloneable marker interface, it signals the compiler that the class allows creation of clones of its objects.

Generally, a marker interface is used with the instanceof operator to check if a reference type variable refers to an object whose class implements the marker interface.