Re: Text Field Max Characters

From:
"John B. Matthews" <nospam@nospam.invalid>
Newsgroups:
comp.lang.java.programmer
Date:
Sat, 09 Oct 2010 23:29:36 -0400
Message-ID:
<nospam-E14FC6.23293509102010@news.aioe.org>
In article
<683f43c0-6f81-423c-aa7d-99d39c81d40a@n16g2000vbg.googlegroups.com>,
 bruce <bruceaj@bellsouth.net> wrote:

Is there any way to set the maximum number of characters a text field
can accept? I used setColumns() and then I used validate(). Didn't
seem to have any effect.


These would affect the field's view; you want to limit the number of
characters permitted in the field's model.

The only other idea I had was to capture the keystrokes and then test
the input for the string length I want to limit the field to. In my
case, that would be overkill!!!!


It seems straightforward; here's an <http://sscce.org/>:

import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.PlainDocument;

/** @author John B. Matthews */
public class ShortDocumentTest extends JPanel {

    private static final int MAX = 8;

    public ShortDocumentTest() {
        this.add(new JTextField(new ShortDocument(), "12345678", MAX));
    }

    private static final class ShortDocument extends PlainDocument {

        @Override
        public void insertString(int offs, String str, AttributeSet a)
                throws BadLocationException {
            if (this.getLength() + str.length() <= MAX) {
                super.insertString(offs, str, a);
            }
        }
    }

    private void display() {
        JFrame f = new JFrame("ShortDocumentTest");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(this);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                new ShortDocumentTest().display();
            }
        });
    }
}

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