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Whatever. There were two panels being shown in the same place. The blank one blocked the other one from view. The fact that the variable center had referred to both of them wasn't relevant. There...

Move the call to setVisible to after you have built the GUI.
Also add code to exit the JVM when the frame is closed.

No, reusing a reference variable should be allowed.
Its the not removing the component that is the problem.

Without code to work with, I don't see how to do anything.

Ok, just noticed the other code and have been able to reproduce your problem.
Look at the components that are added and removed from the...

Can you make a small simple program that compiles and executes to demonstrate the problem?