Exception in thread "main" java.lang.NullPointerException

Question

public static void main(String args[]){
        java.awt.EventQueue.invokeLater(() -> {
            daftar_timbang daftim = new daftar_timbang();
        });
        txtCoba.setText("a");
    }

 

 it shows

Exception in thread "main" java.lang.NullPointerException

 

and, txtCoba is a static jtextfield

help me to get rid of that