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When there is nothing to implement in the marker interfaces like Serializable What is the use of implementing it?
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Marker interface is used as a tag that inform the Java compiler by a message so that it can add some special behavior to the class implementing it.
It is an empty interface (no field or methods). Examples of marker interface are Serializable, Cloneable and Remote interface. All these interfaces are empty interfaces.
Category 1: Marker Annotations The only purpose is to mark a declaration. These annotations contain no members and do not consist of any data. Thus, its presence as an annotation is sufficient. Since the marker interface contains no members, simply determining whether it is present or absent is sufficient.
It has three types: Serializable interface. Cloneable interface. Remote interface.
Joshua Bloch: Effective Java 2nd Edition, p 179
Item 37: Use marker interfaces to define types
... You may hear it said that marker annotations (Item 35) make marker interfaces obsolete. This assertion is incorrect. Marker interfaces have two advantages over marker annotations. First and foremost, marker interfaces define a type that is implemented by instances of the marked class; marker annotations do not. The existence of this type allows you to catch errors at compile time that you couldn’t catch until runtime if you used a marker annotation....
Personally I think I'll bow to Joshua's superior knowledge on this subject.
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In earlier versions of Java, Marker Interfaces were the only way to declare metadata about a class. For example, the Serializable Marker Interface lets the author of a class say that their class will behave correctly when serialized and deserialized.
In modern Java, marker interfaces have no place. They can be completely replaced by Annotations, which allow for a very flexible metadata capability. If you have information about a class, and that information never changes, then annotations are a very useful way to represent it.
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