NumberFormat percentDisplayFormat = NumberFormat.getPercentInstance();
NumberFormat editFormat = NumberFormat.getNumberInstance();

percentDisplayFormat.setMinimumFractionDigits(2);

NumberFormatter percentEditFormatter = new NumberFormatter(editFormat);

JFormattedTextField jftfPercentage = new JFormattedTextField(new DefaultFormatterFactory(new NumberFormatter(percentDisplayFormat), new NumberFormatter(percentDisplayFormat), percentEditFormatter));

jftfPercentage.setBounds(113, 95, 236, 21);
jftfPercentage.setName("JftfPercentage");

jftfPercentage.setValue(<someDoubleValue>);