question: @ Override public boolean addEntry ( Principal caller , AclEntry entry ) throws NotOwnerException { if ( ! isOwner ( caller ) ) throw new NotOwnerException ( ) ; if ( entryList . contains ( entry ) ) return false ; entryList . addElement ( entry ) ; return true ; }
target:  Adds an ACL entry to this ACL. An entry associates a principal (e.g., an individual or a group) with a set of permissions. Each principal can have at most one positive ACL entry (specifying permissions to be granted to the principal) and one negative ACL entry (specifying permissions to be denied). If there is already an ACL entry of the same type (negative or positive) already in the ACL, false is returned.