question: @ Override public boolean equals ( Object o ) { if ( this == o ) { return true ; } if ( o == null || getClass ( ) != o . getClass ( ) ) { return false ; } Account account = ( Account ) o ; if ( username != null ? ! username . equals ( account . username ) : account . username != null ) { return false ; } return true ; }
target:  equals and hashCode use `username` instead of accountId for easier testing. username is unique so it is safe