warning: [serial] serializable class SomeClass has no definition of serialVersionUID

This warning comes when you derive from a class that implements Serializable. In your case, the Serializable parent class is JFrame.

You can suppress this warning with @SuppressWarnings(“serial”), or give the class a serialVersionUID: private static final long serialVersionUID = ...; (with a long value for the dots).

There is a discussion here on SO on which is preferable.