JavaFX TextField Only Numbers

JavaFX TextField is commonly used to take input from users. Sometimes, we may want to restrict the input to only numbers. In this article, we will discuss how to achieve this in JavaFX.

Using TextFormatter

JavaFX provides us with TextFormatter class that can be used to modify the text in a TextField. We can use a regular expression to limit the input to only numbers. Here is an example:

TextField textField = new TextField();
textField.setTextFormatter(new TextFormatter<>(change -> {
    String text = change.getText();
    if (text.matches("[0-9]*")) {
        return change;
    }
    return null;
}));

In the above code, we created a new TextField and set a TextFormatter on it. The TextFormatter takes a UnaryOperator<TextFormatter.Change> as a parameter. The UnaryOperator is a functional interface that takes an argument and returns a result. In our case, the argument is a TextFormatter.Change and the result is also a TextFormatter.Change.

Inside the UnaryOperator, we get the new text that the user entered using change.getText(). We then check if the text contains only numbers using a regular expression [0-9]*. If the text contains only numbers, we return the unchanged TextFormatter.Change. If the text contains anything other than numbers, we return null which prevents the text from being changed.

Using EventHandler

We can also restrict the input to only numbers using EventHandler. Here is an example:

TextField textField = new TextField();
textField.addEventFilter(KeyEvent.KEY_TYPED, event -> {
    if (!event.getCharacter().matches("[0-9]")) {
        event.consume();
    }
});

In the above code, we added an EventHandler KeyEvent.KEY_TYPED to the TextField. The EventHandler takes a KeyEvent as a parameter. Inside the EventHandler, we check if the character typed by the user is a number using a regular expression [0-9]. If the character is not a number, we consume the event using event.consume() which prevents the character from being entered in the TextField.

Conclusion

In this article, we discussed how to restrict the input to only numbers in JavaFX TextField. We saw how to achieve this using TextFormatter and EventHandler. By restricting the input to only numbers, we can improve the user experience and prevent invalid data from being entered in the TextField.