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A marker interface is used to inadvertantly introduce a design flaw.
A marker interface is typically better described as "metadata" with some contractual properties associated with it.
For example, you could eliminate the java.io.Serializable marker interface and introduce a Serializable annotation with associated contract (i.e. in the javadoc), since it is annotations that are the correct tool for metadata, and prior to 1.5, mere javadoc; it has never been interfaces, despite the flaws that are evident in the core API.
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