Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: adding a window to a container
        at java.awt.Container.addImpl(Container.java:1022)
        at java.awt.Container.add(Container.java:935)
        at javax.swing.JFrame.addImpl(JFrame.java:545)
        at java.awt.Container.add(Container.java:352)
        at Lab.createAndShowGUI(Lab.java:470)
        at Lab.access$300(Lab.java:15)
        at Lab$1.run(Lab.java:483)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)