Here's how to go through and interpret the error message:
Exception in thread "main" java.lang.StackOverflowError
at sun.awt.windows.WToolkit.getScreenInsets(Native Method)
at sun.awt.windows.WToolkit.getScreenInsets(Unknown Source)
at sun.java2d.SunGraphicsEnvironment.getUsableBounds(Unknown Source)
at java.awt.GraphicsEnvironment.getCenterPoint(Unknown Source)
at java.awt.Window.setLocationRelativeTo(Unknown Source)
at view.JanelaPrincipal.show(JanelaPrincipal.java:70)
at java.awt.Component.show(Unknown Source)
at java.awt.Component.setVisible(Unknown Source)
at java.awt.Window.setVisible(Unknown Source)
at view.JanelaPrincipal.show(JanelaPrincipal.java:72)
at java.awt.Component.show(Unknown Source)
at java.awt.Component.setVisible(Unknown Source)
at java.awt.Window.setVisible(Unknown Source)
at view.JanelaPrincipal.show(JanelaPrincipal.java:72)
Stack overflow errors usually come from a method that calls itself and never returns. Looking at the stack trace, you start at the top. This line shows you the first place an error was detected. It is often deep in some code you don't know. The next line is the line of code that called the line above, that is, the code in line two called the code in line one.
Now scan down the stack trace. Look for your program name. It will be fully qualified, so the package name will be first. I've highlighted the lines that contain your program's code. Notice that first line 70 is called, but then line 72 is called from line 72...
So line 72 somehow is "calling itself." From the stack trace just below your program line 72, you can see that the method
show is being called. But program line 72 of your program is in the method
show!
So there is your problem. Program line 72 sets visibility, which calls the
show method, that sets visibility, that calls the
show method...