Currently, JSR 114 specification does not say much about the the way of instantiation of rowset implementation classes. There are a some words about that in "2.0 Standard RowSet Definitions":
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JdbcRowSet - A wrapper around a ResultSet object that makes it possible to use the result set as a JavaBeansTM component.
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CachedRowSet - A CachedRowSet object is a JavaBeansTM component that is scrollable, updatable, serializable, and generally disconnected from the source of its data.
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The spec says that classes suppose to be JavaBean component which implies that rowset class should have a default constructor. Such implicit definition may cause incompatibility between different JSR 114 implementations.