如何防止Java中的无头异常？

I have an Applet and when I try to run it on my laptop, a headless exception is thrown by Java at the line where a JFrame is created. Now I know why the JFrame normally causes the exception but my computer was not in headless mode to begin with. I'm also still not sure what headless mode entails exactly.I have an Applet and when I try to run it on my