public class FXNDigitsField extends TextField
{
private long m_digit;
public FXNDigitsField()
{
    super();
}
public FXNDigitsField(long number)
{
    super();
    this.m_digit = number;
    onInitialization();
}

private void onInitialization()
{
    setText(Long.toString(this.m_digit));
}

@Override
public void replaceText(int startIndex, int endIndex, String text)
{
    if (text.matches(Constants.DIGITS_PATTERN) || text.equals(Constants.EMPTY_STRING)) {
        super.replaceText(startIndex, endIndex, text);
    }
}

@Override
public void replaceSelection(String text)
{
    if (text.matches(Constants.DIGITS_PATTERN) || text.equals(Constants.EMPTY_STRING)) {
        super.replaceSelection(text);
    }
}
}

// restrict key input to numerals.
this.addEventFilter(KeyEvent.KEY_TYPED, new EventHandler<KeyEvent>() {
  @Override public void handle(KeyEvent keyEvent) {
    if (!"0123456789".contains(keyEvent.getCharacter())) {
      keyEvent.consume();
    }
  }
});

tyr{
    Integer.parseInt(myNumField.getText());
}catch(Exception e){
    System.out.println("Non-numeric character exist");
}

textField.getTextProperty().addListener(
  (observable, oldValue, newValue) -> {
    if (newValue.equals(oldValue)) return;
      // your validation rules, anything you like
    // do whatever you want with newValue
      // if value is not valid for your rules
    ((StringProperty)observable).setValue(oldValue);
      // or if you want to change something in text when
      // it is valid for you with some changes that can be automated
      // for example change it to upper case
    ((StringProperty)observable).setValue(oldValue.toUpperCase());
  }
);