Threads yielding;

Question

I'm new to this forum so I don't know if it's frowned upon to post lengthy(for me anyway!) code snippets. If it is tell me and I won't do it again.
Anyway.............
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import javax.swing.border.*;
public class Viewer extends JFrame{
DisplayPanel[] panels;
DisplayThread[] display_Threads;
boolean[] running;
int selected;
DisplayListener listener;
public Viewer(){
Container contentPane = getContentPane();
contentPane.setLayout(new BorderLayout());
JPanel topPanel = new JPanel();
JLabel topLabel = new JLabel("Viewer");
topPanel.add(topLabel);
listener = new DisplayListener();
JPanel mainPanel = new JPanel(new GridLayout(1,2));
contentPane.add("North", topPanel);
contentPane.add("Center", mainPanel);
panels = new DisplayPanel[2];
display_Threads = new DisplayThread[2];
running = new boolean[2];
for (int i = 0; i < display_Threads.length; i++){
panels[i] = new DisplayPanel("Panel " + (i + 1));
panels.addMouseListener(listener);
running[i] = false;
mainPanel.add(panels[i]);
setSize(400, 400);
setVisible(true);
addWindowListener(new WindowAdapter(){
public void windowClosing(WindowEvent e){
System.exit(0);
class DisplayListener extends MouseAdapter{
public void mousePressed(MouseEvent e){
if (e.getSource().toString().equals("Panel 1")) {
selected = 0;
if (!running[selected]) {
display_Threads[selected] = new DisplayThread();
display_Threads[selected].start();
running[selected] = true;
else {
display_Threads[selected] = null;
running[selected] = false;
else {
selected = 1;
if (!running[selected]) {
display_Threads[selected] = new DisplayThread();
display_Threads[selected].start();
running[selected] = true;
else {
display_Threads[selected] = null;
running[selected] = false;
class DisplayThread extends Thread{
public DisplayThread(){
public void run(){
Thread currentThread = Thread.currentThread();
while (display_Threads[selected] == currentThread){
try{
Thread.sleep(100);
} catch (InterruptedException e) {}
panels[selected].updatePosition();
panels[selected].repaint();
public static void main(String[] args){
Viewer viewer = new Viewer();
class DisplayPanel extends JPanel{
String name;
int x, y, vel;
public DisplayPanel(String name){
this.name = name;
x = y = 50;
setBackground(Color.lightGray);
setForeground(Color.black);
setBorder(new LineBorder(new Color(204, 204, 204), 3));
public void paintComponent(Graphics g){
super.paintComponent(g);
g.drawString(name, 50+vel, 50);
System.out.println("Paint");
public String toString(){
return name;
public void updatePosition(){
vel++;
When I click on Panel 1 the "Panel 1" string scrolls across the screen.
When I cli1ck on Panel 2 , the first string stops scrolling and the second one starts.
Why does the first one stop when I haven't stopped the Thread.
I'm wondering how to get them both to keep moving at the same time.
Any ideas?

Answer 1

I'm new to this forum so I don't know if it's frowned
upon to post lengthy(for me anyway!) code snippets. If
it is tell me and I won't do it again.
Anyway.............
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import javax.swing.border.*;
public class Viewer extends JFrame{
   DisplayPanel[] panels;
   DisplayThread[] display_Threads;
   boolean[] running;
//why create an array of panels, threads, and boolean?
   int selected;
//what does the selected variable do?
   DisplayListener listener;
//ok, this is a listener class
//contructor
   public Viewer(){
     Container contentPane = getContentPane();
     contentPane.setLayout(new BorderLayout());
     JPanel topPanel = new JPanel();
     JLabel topLabel = new JLabel("Viewer");
     topPanel.add(topLabel);
//what does the DisplayListener class do?
     listener = new DisplayListener();
JPanel mainPanel = new JPanel(new
new GridLayout(1,2));
     contentPane.add("North", topPanel);
     contentPane.add("Center", mainPanel);
//creating an array of data members is gettin me lost?  Why not create an array classes that has all the variables you need for a single object?
     panels = new DisplayPanel[2];
     display_Threads = new DisplayThread[2];
     running = new boolean[2];
     for (int i = 0; i < display_Threads.length; i++){
panels[i] = new DisplayPanel("Panel " + (i +
  (i + 1));
       panels.addMouseListener(listener);
running[i] = false;
mainPanel.add(panels[i]);
setSize(400, 400);
setVisible(true);
addWindowListener(new WindowAdapter(){
public void windowClosing(WindowEvent e){
System.exit(0);
class DisplayListener extends MouseAdapter{
public void mousePressed(MouseEvent e){
if (e.getSource().toString().equals("Panel 1"))
"1")) {
selected = 0;
if (!running[selected]) {
display_Threads[selected] = new
ed] = new DisplayThread();
display_Threads[selected].start();
running[selected] = true;
else {
display_Threads[selected] = null;
running[selected] = false;
else {
selected = 1;
if (!running[selected]) {
display_Threads[selected] = new
ed] = new DisplayThread();
display_Threads[selected].start();
running[selected] = true;
else {
display_Threads[selected] = null;
running[selected] = false;
This is your thread class. The run dedicates what the thread does. Now, you are probably creating only one thread. What not create two threads? One thread in your code only operates one GUI, panel, or frame at a time. So, create two threads. Panel1 would be handle by thread1. Panel2 would be handle by thread2. Now, it comes down to the run method. The ran method can be modified to tell the thread which GUI to handle.
class DisplayThread extends Thread{
public DisplayThread(){
public void run(){
Thread currentThread = Thread.currentThread();
while (display_Threads[selected] ==
== currentThread){
try{
Thread.sleep(100);
} catch (InterruptedException e) {}
panels[selected].updatePosition();
panels[selected].repaint();
public static void main(String[] args){
Viewer viewer = new Viewer();
class DisplayPanel extends JPanel{
String name;
int x, y, vel;
public DisplayPanel(String name){
this.name = name;
x = y = 50;
setBackground(Color.lightGray);
setForeground(Color.black);
setBorder(new LineBorder(new Color(204, 204, 204),
4), 3));
public void paintComponent(Graphics g){
super.paintComponent(g);
g.drawString(name, 50+vel, 50);
System.out.println("Paint");
public String toString(){
return name;
public void updatePosition(){
vel++;
When I click on Panel 1 the "Panel 1" string scrolls
across the screen.
When I cli1ck on Panel 2 , the first string stops
scrolling and the second one starts.
Why does the first one stop when I haven't stopped he
Thread.
I'm wondering how to get them both to keep moving
the same time.
Any ideas?
You probably only create one thread to handle both
GUI panels. Create two threads instead. One thread
handles Panel1, the other thread handles Panel2.
Again, modifiy your run method to dictact which GUI
to hanle:
For example:
//..in your thread class
void run(boolean whichGUI){
   if (true)
      Panel1 run it!
   else
      Panel2 run it!
}Remember, you need to create two threads for each
panel.