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January 2002



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problem refreshing/updating a JTextField

Posted by David Fashena on January 29, 2002 at 5:39 PM

Hello All,

I have a question about how to update/refresh text components in an applet.

Appended below is a small test applet that approximates Pi numerically. There are two JTextFields, one that is used to input a number of iterations and a second one to show the result.

Because the calculation can take a while, I would like the result JTextField to show "Working" while the calculation is proceeding, and then to show the numerical result when it has been computed.

However, I can't figure out how to update the JTextField before the calculation is done. I include the source below. Thanks in advance for any ideas!

// // width = 500 height = 50>

import java.awt.GridLayout;
import java.awt.event.*;
import javax.swing.*;

public class Pi_applet2 extends JApplet implements ActionListener {

public JTextField its_jtf = new JTextField(null, 20);
public JTextField pi_jtf = new JTextField(null, 20);

JPanel pane = new JPanel();

double pi_est;

public void init() {
pane.setLayout(new GridLayout(1,2));

public void actionPerformed(ActionEvent e) {
double pi_est=0.0;
int its;

// ****** the text "Working..." never appears:
// ( why not??)

String num_str = its_jtf.getText(); // get # of iterations
its = Integer.parseInt(num_str);
pi_est = crunch(its); // do the calculation

public double crunch(int max) {
// numerical estimate of Pi
double b = 1.0, s= 0.0, FOUR = 4.0,fm;
int n, flip = 1;
for (n=0; n< max; n++) {
s += flip*FOUR/b;
b = b+2.0;
flip *= -1;



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