Error creating scriptlet class instance

I created project name "JasperDemo" and class "MyNameScriptlet" on jasper package , than I build the Jar with name JasperDemo.jar

On iReport Designer I already added the classpath of JasperDemo.jar (I put it on the same directory with .jrxml)

last thing I created the Scriptlet and fill the Scriptlet class by : jasper.MyNameScriptlet.

but while it compile it give me error

Error filling print... Error creating scriptlet class instance : jasper.MyNameScriptlet

can someone help me? I am nwe with Jasper
Thank you