Find value of a non-static method of the class itself, in a jfieldtextFocusLost

I have a method created by me that returns a boolean:

  public boolean ValidaNumero() {
    long valor;
    if(NIPCC.isFocusable()){

    if (NIPCC.getText().length() != 0 ) {
        try {
            valor = Long.parseLong(NIPCC.getText());
            return true;
        } catch (NumberFormatException ex) {
            JOptionPane.showMessageDialog(null, "Este campo tem de conter 9 dígitos", "Informação", JOptionPane.INFORMATION_MESSAGE);
            NIPCC.grabFocus();
            return false;

        }
    }
    if(NIPCC.getText().length() != 9){
         JOptionPane.showMessageDialog(null, "Este campo tem de conter 9 dígitos", "Informação", JOptionPane.INFORMATION_MESSAGE);
    }
    return false;
    }
    return true;
}

Now in the default java method I have to do the number validation:

private void NIPCCFocusLost(java.awt.event.FocusEvent evt) {                                
    // TODO add your handling code here:


    ValidaNumero();

    if (!NIPCC.getText().substring(0, 1).equals("1") && !NIPCC.getText().substring(0, 1).equals("2")
            && !NIPCC.getText().substring(0, 1).equals("3") && !NIPCC.getText().substring(0, 1).equals("5")
            && !NIPCC.getText().substring(0, 1).equals("6") && !NIPCC.getText().substring(0, 1).equals("8")
            && !NIPCC.getText().substring(0, 1).equals("9")) {
        JOptionPane.showMessageDialog(null, "NIPC inválido!");
    }

The point is that I just want the program to proceed if the return of the ValidaNumber () method is true. I've tried using 'nomeclasse.ValidaNumero ()' to try to know what value was returned, but I can not do it. I was thinking of something like:

do{ ValidaNumero();while(return false);

Is there a way to do this?

I'm trying to solve another problem that is as follows:

The idea is to know if what was written in a jFieldText are not characters and if it has exactly 9 digits, but I have a problem:

public void ValidaNumero() {
        long valor;

        if (NIPCC.getText().length() != 9) {
            for (char letra : NIPCC.getText().toCharArray()) {
                if (letra < '0' || letra > '9') {


                }

            }
            NIPCC.requestFocus();
            JOptionPane.showMessageDialog(null, "Este campo tem de conter 9 dígitos", "Informação", JOptionPane.INFORMATION_MESSAGE);
             }
        else{
            System.out.println("Contém 9 dígitos");
        }
    }

When I enter less than two digits or characters, this code is double-clicked and the error message appears twice, can you explain why?