Using Document FIlter to filter multiple periods(.)

Question

Lets say a user has to input a Double value into the Jtextfield which then gets calculated.
But if the user suddenly used more than 1 period it would trigger a NumberFormatException, so i assume the solution would be using a Document Filter to filter out any extra periods or catching the exception and notifying the user of an invalid input

Currenty using a DocumentFilter to only allow digits and periods, but my problem is how to filter out a second period

PlainDocument filter = new PlainDocument();
            filter.setDocumentFilter(new DocumentFilter() {
                    @Override
                    public void insertString(FilterBypass fb, int off, String str, AttributeSet attr) 
                    throws BadLocationException 
                    {
                    fb.insertString(off, str.replaceAll("[^0-9.]", ""), attr);
                    } 
                    @Override
                    public void replace(FilterBypass fb, int off, int len, String str, AttributeSet attr) 
                    throws BadLocationException 
                    {
                    fb.replace(off, len, str.replaceAll("[^0-9.]", ""), attr);
                    }
            });

            apm.setDocument(filter);

Example

Invalid INPUT: 1.2.2

Valid INPUT: 1.22

no idea talking about, works for me, for better help sooner post an [SSCCE](http://sscce.org/), short, runnable, compilable — mKorbel, Oct 06 '13 at 18:02
I would code the filter to simply not allow a second period. What have you tried? How isn't it working? And hello @mKorbel! — Hovercraft Full Of Eels, Oct 06 '13 at 18:02
@HovercraftFullOfEels - im also using a DocumentListener to calculate for the value. — JLawrence, Oct 06 '13 at 18:57
@HovercraftFullOfEels - how would i filter off the second period? — JLawrence, Oct 06 '13 at 18:59
By parsing String in try/catch and catching NumberFormatException. If no exception, accept the parsed number. If exception, then in catch block return original number and notify user. — Hovercraft Full Of Eels, Oct 06 '13 at 19:08
Or use a `JFormattedTextField` as shown [here](http://stackoverflow.com/a/13424140/1076463) — Robin, Oct 06 '13 at 19:11
Yep, or use an InputVerifier as outlined [here](http://docs.oracle.com/javase/tutorial/uiswing/misc/focus.html). — Hovercraft Full Of Eels, Oct 06 '13 at 19:21
Filtering out the additional '.' is really bad. You can never know what the user intended. i.e.: is '1.2.2' -> '12.2' or '1.22'. Best to let the user enter only correct numbers. — Viktor Seifert, Oct 07 '13 at 08:53

score 0 · Answer 1 · answered Oct 06 '13 at 18:04

Yes, use a try catch block. Implement the happy path (i.e. correctly formatted number) inside the try block and implement the error case in the catch block. For example, if you want to highlight the box in red or pop up an error message, you would put that logic in (or call it from) the catch block.

score 0 · Accepted Answer · answered Jun 06 '15 at 07:35

My suggestion is that you could change the overridden insertString and replace methods so that it checks whether any "." has been inserted earlier before this insert or replace and change the filter in a way that the 'period' would be replaced by a blank string if any subsequent time the period character is inserted by the user. I have illustrated as below:

@Override
public void insertString(FilterBypass fb, int off, String str, AttributeSet attr) 
                throws BadLocationException {
    String regExp;
    Document doc = fb.getDocument();
    if(doc.getText(0, doc.getLength()).indexOf(".") == -1){
        regExp = "[^0-9.]";
    } else {
        regExp = "[^0-9]";
    }
    fb.insertString(off, str.replaceAll(regExp, ""), attr);
}

@Override
public void replace(FilterBypass fb, int off, int len, String str, AttributeSet attr) 
                throws BadLocationException {
    String regExp;
    Document doc = fb.getDocument();
    if(doc.getText(0, doc.getLength()).indexOf(".") == -1){
        regExp = "[^0-9.]";
    } else {
        regExp = "[^0-9]";
    }
    fb.replace(off, len, str.replaceAll(regExp, ""), attr);
}

The above code will only allow the 'period' to be inserted just once in the Document to which this DocumentFilter is set.

Using Document FIlter to filter multiple periods(.)

2 Answers2