Want JTextField outputting a char[] instead of String. (Similar to JPasswordField)

[Chris Kimball]

I'd like to be able to enter multi-line text into an application, yet not have the text returned as a String. Instead I'd like it to be returned as a clearable char[]. JPasswordField allows a char[] output, but, alas, is for single line only.

[Michael Dunn]

read the methods of the String class, what you seek is there.

[Paul Clapham]

And welcome to the Ranch, Chris!

[Chris Kimball]

The problem isn't in converting a String to a char[]. It's having an unclearable, immutable String representation of the text in memory. That's why the JPasswordField class has a char[] output and the String outputs are deprecated.

To demonstrate String x = "Secret" isn't cleared by a subsequent x = "" statement. The String content "Secret" is no longer accessible, but it's somewhere on the computer. With a char[], the data can be overwritten and the original contents are lost and gone forever, as intended.

Thanks,

Chris

[Darryl Burke]

JPasswordField extends JTextField, so maybe you could write your own PasswordArea by extending JTextArea along the same lines.

[Rob Spoor]

Just use a JPasswordField. From the Javadoc comment of its setEchoChar method:

Setting a value of 0 indicates that you wish to see the text as it is typed, similar to the behavior of a standard JTextField.

[Chris Kimball]

The suggestion of extending JTextArea seemed pretty complicated.

JTextComponent is a predecessor of JTextField and offers a getDocument() method. If I retrieve the Document, then the Document getText(int, int, Segment) is available. In Segment a char[] of text is a field. Presumably I could copy the text as a char[] from that field and put trash back into the field's char[] afterwards.

The javax.swing.text.Segment docs says "It should be treated as immutable even though the array is directly accessible. This gives fast access to fragments of text without the overhead of copying around characters. This is effectively an unprotected String. "

Was this what was suggested and does this seem a reasonable approach?

Thanks,

Chris

[Rob Spoor]

If you take a look at the source code of JPasswordField (available in the src.zip file inside your JDK installation folder), you will see that getPassword() is implemented like this:

    public char[] getPassword() {
        Document doc = getDocument();
        Segment txt = new Segment();
        try {
            doc.getText(0, doc.getLength(), txt); // use the non-String API
        } catch (BadLocationException e) {
            return null;
        }
        char[] retValue = new char[txt.count];
        System.arraycopy(txt.array, txt.offset, retValue, 0, txt.count);
        return retValue;
    }

As you see, that indeed uses a Segment. The BadLocationException shouldn't occur unless someone is not respecting the Swing threading rules (from Concurrency in Swing).

FYI, getText() is inherited from JTextComponent and is implemented like this:

    public String getText() {
        Document doc = getDocument();
        String txt;
        try {
            txt = doc.getText(0, doc.getLength());
        } catch (BadLocationException e) {
            txt = null;
        }
        return txt;
    }

[Chris Kimball]

Thanks for your assistance! Also, I didn't know I had the source code.

Chris