Definition
An empty interface having no methods or fields/constants is called a marker interface or a tag interface. This of course means if the interface is extending other interfaces (directly or indirectly) then the super interfaces must not have any inheritable member (method or field/constant) as otherwise the definition of the marker interface (an entirely empty interface) would not be met. Since members of any interface are by default 'public' so all members will be inheritable and hence we can say for an interface to be a marker interface, all of its direct or indirect super interfaces should also be marker. (Thanks marco for raising the point. I thought it was obvious, but mentioning all this explicitly would probably help our readers.)
There are few Java supplied marker interfaces like Cloneable, Serializable, etc. One can create their own marker interfaces the same way as they create any other interface in Java.
An empty interface having no methods or fields/constants is called a marker interface or a tag interface. This of course means if the interface is extending other interfaces (directly or indirectly) then the super interfaces must not have any inheritable member (method or field/constant) as otherwise the definition of the marker interface (an entirely empty interface) would not be met. Since members of any interface are by default 'public' so all members will be inheritable and hence we can say for an interface to be a marker interface, all of its direct or indirect super interfaces should also be marker. (Thanks marco for raising the point. I thought it was obvious, but mentioning all this explicitly would probably help our readers.)
There are few Java supplied marker interfaces like Cloneable, Serializable, etc. One can create their own marker interfaces the same way as they create any other interface in Java.
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