An object that implements the java.security.Principal interface typically also implements this interface to provide a means for comparing that object to a specified Subject.

The comparison is achieved via the implies method. The implementation of the implies method determines whether this object "implies" the specified Subject. One example application of this method may be for a "group" object to imply a particular Subject if that Subject belongs to the group. Another example application of this method would be for "role" object to imply a particular Subject if that Subject is currently acting in that role.

Although classes that implement this interface typically also implement the java.security.Principal interface, it is not required. In other words, classes may implement the java.security.Principal interface by itself, the PrincipalComparator interface by itself, or both at the same time.