Very funny problem, with Swing, please tell me WHY

Question

Hi, guys ,
It seems very funny to me when developog a chat application.
when every time, user enter the text and hit the Enter (through a listener), the text shows up at the screen, and if more texts than the screen, the screen will always focus at the bottom line.
Hwoever, if you do the same but not via a actionPerformed method,(i.e. a for loop in the main metho) the screen will always focus on the first line of the jTextPane.
have a try:
this code will make the focus on the first line, but if you uncomment the thing in the actionPerformed method, and comment one in the main method, if will be totally different
Please tell me WHY
import javax.swing.event.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.text.*;
public class Pane extends JFrame {
JTextPane txtOutput ;
StyledDocument document;
Style normalStyle;
JTextField jf;
public Pane()
Container cont = getContentPane();
cont.setLayout(new BorderLayout());
txtOutput = new JTextPane();
jf = new JTextField(80);
document = txtOutput.getStyledDocument();
// Define style for outputStyle
normalStyle = document.addStyle("Normal", null);
StyleConstants.setItalic(normalStyle, false);
StyleConstants.setFontFamily(normalStyle, "Courier");
StyleConstants.setFontSize(normalStyle, 14);
StyleConstants.setForeground(normalStyle, Color.red);
// Now to insert string at end
txtOutput.setEditable(false);
cont.add(new JScrollPane(txtOutput),BorderLayout.CENTER);
cont.add(jf,BorderLayout.SOUTH);
cont.setVisible(true);
cont.setBounds(100,300,400,500);
jf.addActionListener(
new ActionListener() {
public void actionPerformed (ActionEvent event)
//int i = 50;
//while(i>0){
//setText1("gegegeg");
//i--;
public void setText1(String event) {
String s= event;
//s = jf.getText();
try{
document.insertString(document.getLength(), s+"\n\n" , normalStyle );
catch (Exception e) {
System.out.println("askdf "+e);
public static void main(String args[])
Pane p = new Pane();
p.show();
System.out.println("I am finish");
int i = 50;
while(i>0){
setText1("gegegeg");
i--;
}

Answer 1

I dunno why, why is it important? if you want it to focus on the last line, just always put a code that makes it focus on the last line, and that's it