IllegalArgumentException in JFormattedTextField

Question

I need to make custom text field which will format numeric values according to local way of formatting. So I've made a clas:

public class NumberTextField extends JFormattedTextField 
{...

constructor looks this like:

  public NumberTextField()
   {

    formater=new NumberFormatter();
    formater.setAllowsInvalid( false );
    nf=NumberFormat.getInstance();
    formater.setFormat( nf );

    this.setFormatter( formater );    
   }

It ends up with:

Exception in thread "main" java.lang.IllegalArgumentException: Cannot format given Object as a Number
    at java.text.DecimalFormat.format(Unknown Source)
    at java.text.Format.format(Unknown Source)
    at javax.swing.text.InternationalFormatter.valueToString(Unknown Source)
    at javax.swing.JFormattedTextField$AbstractFormatter.install(Unknown Source)
    at javax.swing.text.DefaultFormatter.install(Unknown Source)
    at javax.swing.text.InternationalFormatter.install(Unknown Source)
    at javax.swing.JFormattedTextField.setFormatter(Unknown Source)
    at hr.ikb.nasa.gui.custom.NumberTextField.<init>(NumberTextField.java:65)
    at hr.ikb.nasa.gui.custom.NumberTextField.main(NumberTextField.java:35)

Since google could not offer something usefull I wanted to see what can you say about it. Maybe it has no value to cope with - I tried to put in constructor this.setValue(new Double(0.0d)); or this.setText("0"); - it did not help..

Answer 1

(Per my comment below): Sub-classing JFormattedTextField and calling the protected setFormat method is probably not the correct approach. From the API docs:

"You should not normally invoke this, instead set the AbstractFormatterFactory or set the value."

Instead I would recommend not sub-classing JFormattedTextField but rather create one using the JFormattedTextField(AbstractFormatter) constructor. I'll leave the code from my original response below in case it's useful - I typically use this formatter when the input of a numerical value is optional and hence a blank text field should imply null.

public class BlankAsNullNumberFormatter extends NumberFormatter {
    private static final long serialVersionUID = 5867546077017490042L;

    public BlankAsNullNumberFormatter(Class<? extends Number> numberKlazz) {
        setValueClass(numberKlazz);
    }

    public BlankAsNullNumberFormatter(Class<? extends Number> numberKlazz, NumberFormat format) {
        super(format);
        setValueClass(numberKlazz);
    }

    public String valueToString(Object iv) throws ParseException {
        if (iv == null) {
            return "";
        } else {
            return super.valueToString(iv);
        }
    }

    public Object stringToValue(String text) throws ParseException {
        if ("".equals(text)) {
            return null;
        }

        return super.stringToValue(text);
    }
}