Ma perchè non li leggete i messaggi di errore?!?!

codice:
java.lang.StringIndexOutOfBoundsException : 
String index out of range: -1 at 
java.lang.String.substring(Unknown Source) at
MainProject.Parametri.setServer(Parametri.java:27) at 
MainProject.SchIniziale.<init>(SchIniziale.java:33) at
MainProject.SchIniziale$5.run(SchIniziale.java:169) at
java.awt.event.InvocationEvent.dispatch(Unknown Source) at 
java.awt.EventQueue.dispatchEventImpl(Unknown Source) at 
java.awt.EventQueue.access$000(Unknown Source) at java.awt.EventQueue$1.run(Unknown 
Source) at java.awt.EventQueue$1.run(Unknown Source) at 
java.security.AccessController.doPrivileged(Native Method) at 
java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source) at 
java.awt.EventQueue.dispatchEvent(Unknown Source) at 
java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source) at 
java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source) at 
java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source) at 
java.awt.EventDispatchThread.pumpEvents(Unknown Source) at 
java.awt.EventDispatchThread.pumpEvents(Unknown Source) at 
java.awt.EventDispatchThread.run(Unknown Source)
Stai sforando con gli indici nella classe Parametri alla riga 27.