A problem about a string length of the JTextField.

Question

Hi, all.
I have a problem of check the length of the text in the JTextField. Look at the following program snippet.
import javax.swing.text.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.event.DocumentListener;
import javax.swing.event.DocumentEvent;
public class test extends JFrame
JTextField jTextField1 = new JTextField(50);
static final int MAX_LENGTH = 10;
public static void main(String[] asArgs)
test testFrm = new test();
testFrm.setVisible(true);
class newDocument extends PlainDocument
public void insertString(int offs,String str,AttributeSet a) throws
BadLocationException
String strTmp;
strTmp = jTextField1.getText();
int nSize1 = strTmp.getBytes().length;
int nSize2 = str.getBytes().length;
if(nSize1 + nSize2 > MAX_LENGTH)
return;
else
super.insertString(offs,str,a);
public test() {
try {
jbInit();
catch(Exception e) {
e.printStackTrace();
private void jbInit() throws Exception {
jTextField1.setText("");
this.getContentPane().add(jTextField1, BorderLayout.NORTH);
newDocument myDocument = new newDocument();
jTextField1.setDocument(myDocument);
public void removeUpdate(DocumentEvent e)
jTextField1.setText(sOldStr);
System.out.println("removeUpdate");
Attention please: I want to check the bytes of the inputted string. It is no problem with english string inputting, but if I input a string with other charset such as A Japanese string or a Chinese string, it doesn't work(when your input string is as long as the MAX_LENGTH, it doesn't work well). How can solve it? Thank you very much.

Answer 1

i believe the problem is that you didn't set the font of the JTextField.
I don't know what's the default Font of the JTextField is (i think it's dialog)
the default textfield cannot display chinese character (and mort unicode character - latin 2 - extends and above).
You need to set the font that can handle displaying the CHinese & Japanese characters (however, your application may not work if you port your app to another computer..and they don't have the font that you specified (unless you ship the font with it))
// why are you getting converting the String to byte and then get the length???
int nSize1 = jTextField1.getText( ).length();