it works a bit

src/Factorial.jas

@@ -0,0 +1,51 @@
+.class public Factorial
+.super java/lang/Object 
+
+.method public <init>()V 
+    aload 0
+    invokenonvirtual java/lang/Object/<init>()V
+    return
+.end method
+
+.method public static factorial(I)I ; calc `given`!
+    .limit locals 3
+    .limit stack  5
+    bipush 1 ;
+    istore 0 ; store the parameter `given`
+    bipush 1 ; we start calculating with `p`=1
+    istore 1 ; store `p`
+    bipush 2 ; we start calculating with `j`=1
+    istore 2 ; store `j`
+    loop:
+        ; p *= j
+        iload 1         ; load p
+        iload 2         ; load j
+        imul            ; multiply p and j
+        istore 1        ; store p*j in p
+
+        ; j++
+        iload 2         ; load j
+        bipush 1        ; put a 1 on the stack
+        iadd            ; add j and 1
+        istore 2        ; store j+1 in j
+
+        ; if j<given
+        iload 2         ; load j
+        iload 0         ; load given
+        if_icmplt loop  ; if j < given goto loop
+
+    ; else return given * p
+    iload 0         ; load given
+    iload 1         ; load p
+    imul            ; multiply given and p
+
+    ireturn          ; return given*p
+.end method
+
+.method public static main([Ljava/lang/String;)V
+    .limit locals 1
+    .limit stack  3
+    getstatic     java/lang/System/out Ljava/io/PrintStream;
+    invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V 
+    return
+.end method