Please have a look at the following code
Class mainWindow
Class Preview
The problem is, when I run the application and click on the "Preview" button, it open the window without the output I need and gives this error
Exception in thread "Thread-3" java.lang.NullPointerException
at preview$ThreadClass.run(preview.java:70)
I know what this error means, but I can't find anything which I haven't declared! .... Please help meeee.....>