“Comparison method violates its general contract!” – TimSort and GridLayout

It seems to me like you’ve hit a bug in the JDK since the error seems to come from Swing classes.

Options:

1. Define the property java.util.Arrays.useLegacyMergeSort as true. Either using in your code the line

   System.setProperty("java.util.Arrays.useLegacyMergeSort", "true");
   

   before any Swing code. As the first line in the main method should work.

   Or adding

   -Djava.util.Arrays.useLegacyMergeSort=true
   

   to your starting options (in the console, or in the project properties in an IDE, Ant script, etc.)

2. Upgrade your JDK and see if the problem goes away

3. Downgrade to Java 6