hworld.jas

《java virtual machine》是研究jvm的一本书

;; create a container

(define my-class (make-class-env))


;; specify class hierarchy

(jas-class-setaccess my-class acc-public)
(jas-class-setclass my-class (make-class-cpe "out"))
(jas-class-setsuperclass my-class (make-class-cpe "java/lang/Object"))


;; write a convenience function to append insns as a list.
(define append-code
  (lambda (code-part insn-list)
    (mapcar (lambda (insn) (jas-code-addinsn code-part insn))
            insn-list)))

;; Define code for initializer
;;
(define init-it (make-code))
(append-code
 init-it
 (quote
  ((aload_0)
   (invokenonvirtual (make-method-cpe "java/lang/Object" "<init>" "()V"))
   (return))))

;; this is the code that comprises
;; the actual task, ie the code for
;; main(String argv[]).
;; print a string 5 times

(define doit (make-code))
(append-code
 doit
 (quote
  (

                                        ; store references in local
                                        ; variables to avoid field/cp
                                        ; lookup
   (getstatic
    (make-field-cpe "java/lang/System" "out" "Ljava/io/PrintStream;"))
   (astore_1)
   (ldc (make-string-cpe "Hello World"))
   (astore_2)
   (bipush 5)
   (istore_3)                           ; store loop index in var reg 3

                                        ; loop 5 times, printing out
                                        ; the string.

   (make-label "loop")
                                        ; push arguments to function
                                        ; on stack and call it

   (aload_1) (aload_2)
   (invokevirtual
    (make-method-cpe "java/io/PrintStream" "println" "(Ljava/lang/String;)V"))

                                        ; decrement loop index

   (iinc 3 -1)
   (iload_3)
   (ifne (make-label "loop"))
   (return))))

;; set stack/var size

(jas-code-stack-size doit 3)
(jas-code-var-size doit 4)

;; fill up the class with the methods

;; first the initializer.
(jas-class-addmethod my-class acc-public "<init>" "()V" init-it ())

;; define the printing code as a static main(String argv[]) method

(jas-class-addmethod my-class
                     (| acc-static acc-public)
                     "main" "([Ljava/lang/String;)V" doit ())

;; write it out.

(jas-class-write my-class (make-outputstream "out.class"))