Can not fine symbol... class SwingWorker is not working...

Question

Hi ,
my code is like this. I am using netbeans ide 5.5.
package concurrency;
import java.util.List;
import java.util.Random;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.GridBagLayout;
import java.awt.GridBagConstraints;
import java.awt.Insets;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.border.Border;
import javax.swing.BorderFactory;
import javax.swing.*;
public class Flipper extends JFrame
implements ActionListener {
private final GridBagConstraints constraints;
private final JTextField headsText, totalText, devText;
private final Border border =
BorderFactory.createLoweredBevelBorder();
private final JButton startButton, stopButton;
private FlipTask flipTask;
private JTextField makeText() {
JTextField t = new JTextField(20);
t.setEditable(false);
t.setHorizontalAlignment(JTextField.RIGHT);
t.setBorder(border);
getContentPane().add(t, constraints);
return t;
private JButton makeButton(String caption) {
JButton b = new JButton(caption);
b.setActionCommand(caption);
b.addActionListener(this);
getContentPane().add(b, constraints);
return b;
public Flipper() {
super("Flipper");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Make text boxes
getContentPane().setLayout(new GridBagLayout());
constraints = new GridBagConstraints();
constraints.insets = new Insets(3, 10, 3, 10);
headsText = makeText();
totalText = makeText();
devText = makeText();
//Make buttons
startButton = makeButton("Start");
stopButton = makeButton("Stop");
stopButton.setEnabled(false);
//Display the window.
pack();
setVisible(true);
private static class FlipPair {
private final long heads, total;
FlipPair(long heads, long total) {
this.heads = heads;
this.total = total;
private class FlipTask extends SwingWorker<Void, FlipPair> {
@Override
protected Void doInBackground() {
long heads = 0;
long total = 0;
Random random = new Random();
while (!isCancelled()) {
total++;
if (random.nextBoolean()) {
heads++;
publish(new FlipPair(heads, total));
return null;
@Override
protected void process(List<FlipPair> pairs) {
FlipPair pair = pairs.get(pairs.size() - 1);
headsText.setText(String.format("%d", pair.heads));
totalText.setText(String.format("%d", pair.total));
devText.setText(String.format("%.10g",
((double) pair.heads)/((double) pair.total) - 0.5));
public void actionPerformed(ActionEvent e) {
if ("Start" == e.getActionCommand()) {
startButton.setEnabled(false);
stopButton.setEnabled(true);
(flipTask = new FlipTask()).execute();
} else if ("Stop" == e.getActionCommand()) {
startButton.setEnabled(true);
stopButton.setEnabled(false);
flipTask.cancel(true);
flipTask = null;
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
new Flipper();
Though this code is taken from java.sun.com.
but this code is not working.. It shows :
Compiling 1 source file to F:\ ...\FlipperProject\build\classes
F:\....\FlipperProject\src\concurrency\Flipper.java:73: cannot find symbol
symbol : class SwingWorker
location: class concurrency.Flipper
private class FlipTask extends SwingWorker<Void, FlipPair> {
F:\.......\FlipperProject\src\concurrency\Flipper.java:79: cannot find symbol
symbol : method isCancelled()
location: class concurrency.Flipper.FlipTask
while (!isCancelled()) {
F:\.....\FlipperProject\src\concurrency\Flipper.java:84: cannot find symbol
symbol : method publish(concurrency.Flipper.FlipPair)
location: class concurrency.Flipper.FlipTask
publish(new FlipPair(heads, total));
F:\.......\FlipperProject\src\concurrency\Flipper.java:74: method does not override a method from its superclass
@Override
F:\.......\FlipperProject\src\concurrency\Flipper.java:89: method does not override a method from its superclass
@Override
F:\......1\FlipperProject\src\concurrency\Flipper.java:105: cannot find symbol
symbol : method execute()
location: class concurrency.Flipper.FlipTask
(flipTask = new FlipTask()).execute();
F:\............\FlipperProject\src\concurrency\Flipper.java:109: cannot find symbol
symbol : method cancel(boolean)
location: class concurrency.Flipper.FlipTask
flipTask.cancel(true);
7 errors
BUILD FAILED (total time: 4 seconds)
please help...

Answer 1

try right-clicking on the source and select fix imports.