JTextField accept only valid unsigned Shorts? (Using KeyAdapter)

Question

Below is the KeyAdapter I tried to get working to only accept values less than 65535. It seems as though it gets it one keystroke behind where it actually should. For example, If I type "55", the System.out.println will yield "5", doing "3298" will yield "329", etc.

// Allows for unsigned short values only
KeyAdapter unsignedShortAdapter = new KeyAdapter() {

    public void keyTyped(KeyEvent e) {
        char c = e.getKeyChar();
        int tempInt = 0;
        JTextField temp = null;

        if (!((Character.isDigit(c) || (c == KeyEvent.VK_BACK_SPACE) || (c == KeyEvent.VK_DELETE)))) {
            getToolkit().beep();
            e.consume();
        }
        try {
            temp = (JTextField) e.getSource();
            System.out.println(temp.getText());
            tempInt = (Integer.parseInt(temp.getText().toString()));
        } catch (NumberFormatException e1) {

        } finally {
            if (tempInt > (Short.MAX_VALUE * 2)) {
                 getToolkit().beep();
                 e.consume();
                temp.setText(temp.getText().substring(0, temp.getText().length() - 1));

                invalidate();
            }

        }
    }

};

Do you have to use a `KeyListener`? Cause there are so many better solutions otherwise — MadProgrammer, Aug 11 '12 at 22:05
No, I don't. I want to use whatever I can get to work, haha. I just use KeyListener to prevent users from typing non-number chars. — snotyak, Aug 11 '12 at 22:07
The problem is, you're getting the keystroke BEFORE the text field is been updated, so when your text field contains "5" and you press "5", the field only contains "5" when you trap the key stroke. — MadProgrammer, Aug 11 '12 at 22:10

MadProgrammer · Accepted Answer · 2012-08-12T03:59:30.487

So, instead of a KeyListener, which you've found, is unreliable and will cause lots of nasty side effects (and possible Document Mutation exceptions :P), we should use a DocumentFilter, cause that's what it's designed for

public class ShortFilter extends DocumentFilter {

    protected boolean valid(String text) {


        boolean valid = true;
        for (char check : text.toCharArray()) {

            if (!Character.isDigit(check)) {

                valid = false;
                break;

            }

        }

        if (valid) {

            int iValue = Integer.parseInt(text);

            valid = iValue <= (Short.MAX_VALUE * 2);

        }

        return valid;

    }

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

        StringBuilder sb = new StringBuilder(fb.getDocument().getText(0, fb.getDocument().getLength()));
        sb.insert(offset, text);

        if (valid(sb.toString())) {

            super.insertString(fb, offset, text, attr);

        }

    }

    @Override
    public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attrs) throws BadLocationException {

        if (length > 0) {

            StringBuilder sb = new StringBuilder(fb.getDocument().getText(0, fb.getDocument().getLength()));

            sb.delete(offset, length);
            sb.insert(offset, text);

            if (valid(sb.toString())) {

                super.replace(fb, offset, length, text, attrs);

            }

        } else {

            insertString(fb, offset, text, attrs);

        }

    }
}

You will need to apply this to the field's document

((AbstractDocument) field.getDocument()).setDocumentFilter(new ShortFilter());

I'd check out

For some more info

UPDATE for Decimal inclusion

Basically, if you want to allow the inclusion of a decimal, you need to allow for the character in the valid method.

You also need to check the current document's contents

StringBuilder sb = new StringBuilder(fb.getDocument().getText(0, fb.getDocument().getLength()));

// Update the StringBuilder as per noraml
// Check valid as per normal

if (text.contains(".") && sb.contains(".")) {
  // already have decimal place
} else {
  // Business as usual...
}

How would I go about doing this for a decimal value? Basically asking how I'd limit it to one "." — snotyak, Aug 11 '12 at 22:50
@BackpackOnHead Check the updates, I place some REALLY basic logic in as an example — MadProgrammer, Aug 12 '12 at 03:59

JTextField accept only valid unsigned Shorts? (Using KeyAdapter)

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