JFormattedTextField to format percent numbers?

Question

I would like to format a float number as a percent-value with JFormattedTextField that allows inputs from 0 to 100 percent (converted to 0.0f-1.0f), always shows the percent

Answer 1

Imho https://docs.oracle.com/javase/tutorial/uiswing/components/formattedtextfield.html gives a pretty good example (see section "Specifying Formatters and Using Formatter Factories").

The key is to use a Percent Format to display values and a custom NumberFormatter to edit values. This approach also allows the use of fraction digits.

// create a format for displaying percentages (with %-sign)
NumberFormat percentDisplayFormat = NumberFormat.getPercentInstance();

// create a format for editing percentages (without %-sign)
NumberFormat percentEditFormat = NumberFormat.getNumberInstance();

// create a formatter for editing percentages - input will be transformed to percentages (eg. 50 -> 0.5)
NumberFormatter percentEditFormatter = new NumberFormatter(percentEditFormat) {
    private static final long serialVersionUID = 1L;

    @Override
    public String valueToString(Object o) throws ParseException {
        Number number = (Number) o;
        if (number != null) {
            double d = number.doubleValue() * 100.0;
            number = new Double(d);
        }
        return super.valueToString(number);
    }

    @Override
    public Object stringToValue(String s) throws ParseException {
        Number number = (Number) super.stringToValue(s);
        if (number != null) {
            double d = number.doubleValue() / 100.0;
            number = new Double(d);
        }
        return number;
    }
};

// set allowed range
percentEditFormatter.setMinimum(0D);
percentEditFormatter.setMaximum(100D);

// create JFormattedTextField
JFormattedTextField field = new JFormattedTextField(
    new DefaultFormatterFactory(
        new NumberFormatter(percentDisplayFormat),
        new NumberFormatter(percentDisplayFormat),
        percentEditFormatter));