JFormattedTextField that only allows integers

Question

I've been searching and I can't find a place where I understand how to create a JFormattedTextField that only allows integers as input. Is it even possible?

edit found this code from @HovercraftFullOfEels:

public class QuantFilter extends DocumentFilter {
    @Override
    public void insertString(FilterBypass fb, int offset, String string,
             AttributeSet attr) throws BadLocationException {

          Document doc = fb.getDocument();
          StringBuilder sb = new StringBuilder();
          sb.append(doc.getText(0, doc.getLength()));
          sb.insert(offset, string);

          if (test(sb.toString())) {
             super.insertString(fb, offset, string, (javax.swing.text.AttributeSet) attr);
          }
       }

       private boolean test(String text) {
          try {
             Integer.parseInt(text);
             return true;
          } catch (NumberFormatException e) {
             return false;
          }
       }
       @Override
       public void replace(FilterBypass fb, int offset, int length, String text,
             AttributeSet attrs) throws BadLocationException {

          Document doc = fb.getDocument();
          StringBuilder sb = new StringBuilder();
          sb.append(doc.getText(0, doc.getLength()));
          sb.replace(offset, offset + length, text);

          if (test(sb.toString())) {
             super.replace(fb, offset, length, text, (javax.swing.text.AttributeSet) attrs);
          }
       }

       @Override
       public void remove(FilterBypass fb, int offset, int length)
             throws BadLocationException {
          Document doc = fb.getDocument();
          StringBuilder sb = new StringBuilder();
          sb.append(doc.getText(0, doc.getLength()));
          sb.delete(offset, offset + length);

          if (test(sb.toString())) {
             super.remove(fb, offset, length);
          }
       }
}

The overrides say that it should override a method, and if I take it doesn't enter the insertString()