How to restrict the JTextField to a x number of characters
You should use a DocumentFilter as per this tutorial. For example:
import javax.swing.*;
import javax.swing.text.*;
public class JTextFieldLimit2 extends JPanel{
JTextField textfield = new JTextField(5);
public JTextFieldLimit2() {
PlainDocument doc = (PlainDocument) textfield.getDocument();
doc.setDocumentFilter(new TextLengthDocFilter(3));
add(textfield);
}
private class TextLengthDocFilter extends DocumentFilter {
private int maxTextLength;
public TextLengthDocFilter(int maxTextLength) {
this.maxTextLength = maxTextLength;
}
private boolean verifyText(String text) {
return text.length() <= maxTextLength;
}
@Override
public void insertString(FilterBypass fb, int offset, String string,
AttributeSet attr) throws BadLocationException {
Document doc = fb.getDocument();
String oldText = doc.getText(0, doc.getLength());
StringBuilder sb = new StringBuilder(oldText);
sb.insert(offset, string);
if (verifyText(sb.toString())) {
super.insertString(fb, offset, string, attr);
}
}
@Override
public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attrs)
throws BadLocationException {
Document doc = fb.getDocument();
String oldText = doc.getText(0, doc.getLength());
StringBuilder sb = new StringBuilder(oldText);
sb.replace(offset, offset + length, text);
if (verifyText(sb.toString())) {
super.replace(fb, offset, length, text, attrs);
}
}
@Override
public void remove(FilterBypass fb, int offset, int length) throws BadLocationException {
Document doc = fb.getDocument();
String oldText = doc.getText(0, doc.getLength());
StringBuilder sb = new StringBuilder(oldText);
sb.replace(offset, offset + length, "");
if (verifyText(sb.toString())) {
super.remove(fb, offset, length);
}
}
}
private static void createAndShowUI() {
JFrame frame = new JFrame("JTextFieldLimit2");
frame.getContentPane().add(new JTextFieldLimit2());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
createAndShowUI();
}
});
}
}