JOptionPane o PopUP

Hello, I would like to use a pop up or joption pane to show an alert when a validator executes. I've tried on fields and on message validator but I always get this exception:

Caused by: java.awt.HeadlessException
at java.awt.GraphicsEnvironment.checkHeadless(GraphicsEnvironment.java:159)
at java.awt.Window.(Window.java:432)
at java.awt.Frame.(Frame.java:403)
at java.awt.Frame.(Frame.java:368)

Can anybody help me?

Thanks in advance