proper use of define-alias

[Chuah Teong Leong <teongleong at gmail dot com>]

hi. I'm new to the use of define-alias and I was trying to use it as follows.

Exception:
Value '20' for variable 'vpolicy' has wrong type (java.lang.Integer) (java.lang.
Integer cannot be cast to gnu.mapping.Location)

(define-alias vert-sb-always
<javax.swing.ScrollPaneConstants>:VERTICAL_SCROLLBAR_ALWAYS)
(define-alias vert-sb-needed
<javax.swing.ScrollPaneConstants>:VERTICAL_SCROLLBAR_AS_NEEDED)
(define-alias vert-sb-never
<javax.swing.ScrollPaneConstants>:VERTICAL_SCROLLBAR_NEVER)

(define-alias hori-sb-always
<javax.swing.ScrollPaneConstants>:HORIZONTAL_SCROLLBAR_ALWAYS)
(define-alias hori-sb-needed
<javax.swing.ScrollPaneConstants>:HORIZONTAL_SCROLLBAR_AS_NEEDED)
(define-alias hori-sb-never
<javax.swing.ScrollPaneConstants>:HORIZONTAL_SCROLLBAR_NEVER)

(define (make-scrollpane in-component :: <javax.swing.JComponent>)
  (<javax.swing.JScrollPane> in-component))

;; make a scrollpane with policy
(define (make-scrollpane-with-policy in-component :: <javax.swing.JComponent>
                                     vp-sym :: <symbol>
                                     hp-sym :: <symbol> )

;; choose the correct constant based on the symbol passed in
  (define vpolicy
    (case vp-sym
      ((always) vert-sb-always)
      ((needed) vert-sb-needed)
      ((never) vert-sb-never)
      (else (display "Error unknown policy ")(display vp-sym)
            vert-sb-needed)))

   (define hpolicy
    (case hp-sym
      ((always) hori-sb-always)
      ((needed) hori-sb-needed)
      ((never) hori-sb-never)
      (else (display "Error unknown policy ")(display hp-sym)
            hori-sb-needed)))

   (<javax.swing.JScrollPane> in-component vpolicy hpolicy)
  )

What is the proper way of doing what I want to do here?