Java Number Field
NumberFormat longFormat = NumberFormat.getIntegerInstance();
NumberFormatter numberFormatter = new NumberFormatter(longFormat);
numberFormatter.setValueClass(Long.class); //optional, ensures you will always get a long value
numberFormatter.setAllowsInvalid(false); //this is the key!!
numberFormatter.setMinimum(0l); //Optional
JFormattedTextField field = new JFormattedTextField(numberFormatter);