Structural, and only within one subtype: discriminating on javaClass rather than on the seven fields alone is what keeps a Link from equalling an Article at the same coordinates, since all three carry an identical field set.

hashCode

override fun hashCode(): Int

Consistent with equals, subtype included — but keyed on the class name, never the class. Class inherits the identity hash, which is drawn afresh each time the process starts, so folding it in would give a hash that does not survive a restart. String.hashCode is specified, so this one is the same on every run.

toString

override fun toString(): String

Every property, for logs and crash reports.