Cara Membuat JFrame Tampil di Tengah Layar + Validasi Input (Java NetBeans)

// Mengatur Dimensi center screen
Dimension dim = Toolkit.getDefaultToolkit().getScreenSize();
        int x = (dim.width - getSize().width)/2;
        int y = (dim.height - getSize().height)/2;
        setLocation(x, y);

//filter hanya huruf
   public void FilterHuruf(KeyEvent a){
       if(Character.isDigit(a.getKeyChar())){
           a.consume();
           JOptionPane.showMessageDialog(null, "masukan huruf saja!", "peringatan", JOptionPane.WARNING_MESSAGE);
       }
   }

//filter hanya angka
    public void FilterAngka(KeyEvent a){
       if(Character.isAlphabetic(a.getKeyChar())){
           a.consume();
           JOptionPane.showMessageDialog(null, "masukan angka saja!", "peringatan", JOptionPane.WARNING_MESSAGE);
       }
   }

  // TODO add your handling code here:
        try{
            Desktop.getDesktop().browse(new URL("http://localhost:81/penjualanelektronik/print.php").toURI());
            } catch (Exception e){
                System.out.println(e);
            }