Allow only numbers in JTextfield

Question

I'm trying to implement requirements like:

Accept only numbers in JTextield, when a non-digit key pressed, it will not be accepted.

I tried many stuff, even tried to call the backspace event to remove the last character if it's a non-digit. However, not able to remove the value typed in the textfield. I tried to understand DOCUMENT FILTER but finding it difficult to implement. I will be glad if anyone helps me to resolve the issue.

Answer 1

Use DocumentFilter. Here is simple example with regex:

JTextField field = new JTextField(10);
((AbstractDocument)field.getDocument()).setDocumentFilter(new DocumentFilter(){
        Pattern regEx = Pattern.compile("\\d*");

        @Override
        public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attrs) throws BadLocationException {          
            Matcher matcher = regEx.matcher(text);
            if(!matcher.matches()){
                return;
            }
            super.replace(fb, offset, length, text, attrs);
        }
    });

field is your JTextField, and this filter allow to enter only digits.