限制JTextField中的字符数

Question

I try to limit the number of allowable characters to 5 by using

    try {
        jFormattedTextField2.setFormatterFactory(new javax.swing.text.DefaultFormatterFactory(new javax.swing.text.MaskFormatter("*****")));
    } catch (java.text.ParseException ex) {
        ex.printStackTrace();
    }

However, when I only enter 1 character, there will always be 4 others space being padded. How can I avoid the padding, at the same time limiting number of characters?

Answer 1

JFormattedTextField leads to evil UIs.

The class you want is javax.swing.text.DocumentFilter . This allows you modify mutations in a chain-of-command style.

Answer 2

Instead of a JFormattedTextField, use a plain JTextField. Change the textfield's document to accept only a specific number of characters by setting a custom document.

Answer 3

Great question, and it's odd that the Swing toolkit doesn't include this functionality natively for JTextFields. But, here's a great answer from my Udemy.com course "Learn Java Like a Kid":

txtGuess = new JTextField();
txtGuess.addKeyListener(new KeyAdapter() {
    public void keyTyped(KeyEvent e) { 
        if (txtGuess.getText().length() >= 3 ) // limit textfield to 3 characters
            e.consume(); 
    }  
});

This limits the number of characters in a guessing game text field to 3 characters, by overriding the keyTyped event and checking to see if the textfield already has 3 characters - if so, you're "consuming" the key event (e) so that it doesn't get processed like normal.

Hope that helps :)