When concrete classes are preferrable to interfaces

String vs. CharSequence
- better relays immutability?
- so widespread that it can be an inconvenience to accept a CharSequence and have to do something with it, like pass to another 3rd party library method

Exception vs. Throwable
- error details object in REST application, don't want people to attempt to create these if there's an Error

LocalDate vs. ChronoLocalDate
"Most applications should declare method signatures, fields and variables as LocalDate, not this interface."

StringBuilder/Writeable vs. Appendable