Restrict JTextField to only accept certain characters

Question

I have 4 JTextFields that should only accept certain characters:

binary digits (0, 1)
octal digits, so (0 - 7)
all digits (0 - 9)
all hexadecimal characters (0 - 9, a - f, A - F)

The user must not be able to input a forbidden character.

I know how I could validate the input afterwards, but not how to filter it.

I tried using a MaskFormatter, but then I can't enter anything at all.

MaskFormatter binaryFormatter = new MaskFormatter();
binaryFormatter.setValidCharacters("01");
JFormattedTextField binaryText = new JFormattedTextField(binaryFormatter);

[Implementing a DocumntFilter](https://docs.oracle.com/javase/tutorial/uiswing/components/generaltext.html#filter) and [Examples](http://www.jroller.com/dpmihai/entry/documentfilter) — MadProgrammer, Jun 12 '15 at 22:16
You could pass the formatted text field a [`MaskFormatter`](http://docs.oracle.com/javase/7/docs/api/javax/swing/text/MaskFormatter.html) which specifies valid characters — Dioxin, Jun 12 '15 at 22:16
Convert your requirements into a `java.text.Format`, and use it in combination with the `JFormattedTextField`, as shown [here](http://stackoverflow.com/a/13424140/1076463) — Robin, Jun 13 '15 at 13:25

score 3 · Accepted Answer · answered Jun 12 '15 at 22:24

You don't want to format the value, you want to filter the content. Use a DocumentFilter on a plain on JTextField

Start by having a look at Implementing a DocumntFilter and Examples for more details...

As an example, a "binary filter", which will only accept 0 and 1

public class BinaryDocumentFilter extends DocumentFilter {

    @Override
    public void insertString(DocumentFilter.FilterBypass fb, int offset,
            String text, AttributeSet attr)
            throws BadLocationException {
        StringBuilder buffer = new StringBuilder(text.length());
        for (int i = buffer.length() - 1; i >= 0; i--) {
        char ch = buffer.charAt(i);
        if (ch == '0' || ch == '1') {
            buffer.append(ch);
        }
        }
        super.insertString(fb, offset, buffer.toString(), 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);
    }
}

Which can be applied directly to the field's Document:

JTextField binaryField = new JTextField(10);
((AbstractDocument)binaryField.getDocument()).setDocumentFilter(new BinaryDocumentFilter());

at super.insertString(fb, offset, buffer.toString(), **attr**); — Scriptim, Jun 12 '15 at 22:54
@Scriptim You're importing the wrong `AttributeSet`, you need `javax.swing.text.AttributeSet` and forgive me, but I've been using this technique for more the 15 years and works just fine. The `DocumentFilter` is the best mechanism for restricting (or filtering) content into text components — MadProgrammer, Jun 13 '15 at 00:07

Restrict JTextField to only accept certain characters

1 Answers1