Question

I have a JFormattedTextField using the following mask formatter:

    private MaskFormatter maskForInput;
    maskForInput=new MaskFormatter("####"); // I have tried using stars (*) too.
    maskForInput.setValidCharacters("0123456789");

    javax.swing.JFormattedTextField playerRaiseField=new javax.swing.JFormattedTextField(maskForInput);

This is supposed to allow the user to enter up to 4 digits as an input. However when I am trying to Integer.parseInt(playerRaiseField.getText()) the String returned from this field I am always getting a NumberFormatException possibly due to the empty spaces left on user input.
To clear this up:

If the user inputs 560 for example there is a trailing space left behind so the String I am reading is 560( ) and when trying to parse this String into an int this exception is thrown. Any workarounds? How can I modify the mask formatter to accept 1 to 4 digits and not always 4 digits fixed??

Note: Curiously enough using trim() on the String returned is still not removing the extra whitespace character…

Answer 1

There are a number of things wrong with your expectations…

Firstly, you seem to believe that a formatted field can have any number of characters. This isn’t true (while you can get the text, the field remains in what it considers to be an invalid state). The formatted field expects that the all the places of the mask must be filled.

Secondly, you should be using the JFormattedTextField#getValue method to return the value of the field, not getText

Thirdly, the text being returned is filled with the mask’s placeholder character (MaskFormatter#getPlaceholder), which may or may not be a space, so String#trim probably isn’t going to be of help…

If you want the user to only be able to enter a numeric value, which may consist of 0-n characters, then you really should consider using a DocumentFilter applied to normal JTextField

public class TestField {

    public static void main(String[] args) {
        new TestField();
    }

    public TestField() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (Exception ex) {
                }

                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class NumericDocumentFilter extends DocumentFilter {

        private int maxChars;

        public NumericDocumentFilter(int maxChars) {
            this.maxChars = maxChars;
        }

        @Override
        public void insertString(DocumentFilter.FilterBypass fb, int offset,
                String text, AttributeSet attr)
                throws BadLocationException {

            StringBuilder buffer = new StringBuilder(text);
            for (int i = buffer.length() - 1; i >= 0; i--) {
                char ch = buffer.charAt(i);
                if (!Character.isDigit(ch)) {
                    buffer.deleteCharAt(i);
                }
            }

            text = buffer.toString();
            if (fb.getDocument().getLength() + text.length() > maxChars) {
                int remaining = maxChars - fb.getDocument().getLength();
                text = text.substring(0, remaining);
            }

            if (text.length() > 0) {
                super.insertString(fb, offset, text, attr);
            }
        }

        @Override
        public void replace(DocumentFilter.FilterBypass fb,
                int offset, int length, String string, AttributeSet attr) throws BadLocationException {
            if (length > 0) {
                fb.remove(offset, length);
            }
            insertString(fb, offset, string, attr);
        }
    }

    public class TestPane extends JPanel {

        private JTextField field;

        public TestPane() {

            setLayout(new GridBagLayout());

            field = new JTextField(4);
            ((AbstractDocument) field.getDocument()).setDocumentFilter(new NumericDocumentFilter(4));
            add(field);
            field.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    System.out.println(field.getText());
                }
            });
        }
    }
}