Develop Reference

Does "Thread.sleep()" do anything else than pause the program for a certain amount of time?

I have created a program that draws a thick line.
import javax.swing.*;
import java.awt.*;
public class Movement {
int xGrid = 50;
public static void main(String[] args) {
Movement m = new Movement();
m.animate();
}
public void animate() {
JFrame frame = new JFrame("Movement");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
ScreenDisplay display = new ScreenDisplay();
frame.getContentPane().add(display);
frame.setSize(400, 400);
frame.setVisible(true);
for (int aL = 0; aL < 200; aL++) {
xGrid++;
display.repaint();
try {
Thread.sleep(50);
} catch (Exception ex) { }
}
}
class ScreenDisplay extends JPanel {
public void paintComponent(Graphics g) {
g.setColor(Color.RED);
g.fillOval(xGrid, 175, 50, 50);
}
}
}
Because of the method "Thread.sleep(50)", the speed of the program slows down a little.
So I got a little curious and removed the "sleep()" method.
What I expected to output was the exact same output, just extremely fast.
However, it just prints out one circle in the frame.
I don't really know why it outputs just one circle, none of the researches I've done back up the answer.
Can anyone please explain why?

From Component.repaint documentation:
Repaints this component.
If this component is a lightweight component, this method
causes a call to this component's paint
method as soon as possible. Otherwise, this method causes
a call to this component's update method as soon
as possible.
By the looks of it, your for loop finishes so quickly that by the time the component calls the repaint method, it has already finished and therefore only paints the final circle stored in the buffer.

JFrame and GlassPane - Trouble with repaint()

This question may be a simple matter of me lacking a fundamental understanding of Java Swing or Graphics, and if so, I apologize.
I'm trying to develop a GUI application using Java Swing that can be controlled by an external device that sends pitch, yaw, and roll values via bluetooth to the Application. My idea is to create a cursor (perhaps an empty circle) that moves around when the external device moves around. I have no problems with receiving the data from the device, just the part where I need to actually paint something over all of my components.
I figured that a GlassPane was the easiest way to show a cursor over the entire application, and have it move around when the external device is moved around. I use a Thread to capture the data, and I'm trying to call repaint() afterwards, but it doesn't seem to be triggering.
Here is the relevant code:
JFrame:
public class Frame extends JFrame {
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
//Thread myoHandlerThread = new Thread(myoHandler);
//myoHandlerThread.start();
Frame frame = new Frame();
GlassPane glassPane = new GlassPane();
glassPane.setVisible(true);
frame.setGlassPane(glassPane);
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
public Frame() {
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(50, 50, 1000, 650);
/* Code to add and place components */
}
}
And my GlassPane:
public class GlassPane extends JComponent {
private static double pitch;
private static double yaw;
private static double roll;
Point point;
public void setPoint(Point p) {
this.point = p;
}
public void paintComponent(Graphics g) {
if (point != null) {
System.out.println("Test print statement");
g.setColor(Color.red);
g.fillOval(point.x - 10, point.y - 10, 20, 20);
}
}
public GlassPane() {
Thread handler = new Thread(deviceHandler);
handler.start();
}
private Runnable deviceHandler = new Runnable() {
#Override
public void run() {
Hub hub = new Hub("com.garbage");
System.out.println("Attempting to find device...");
Device externalDevice = hub.waitForDevice(10000);
if (externalDevice == null) {
throw new RuntimeException("Unable to find device!");
}
System.out.println("Connected");
DataCollector dataCollector = new DataCollector();
hub.addListener(dataCollector);
while (true) {
hub.run(1000/20); //gathers data and stores in dataCollector
roll = dataCollector.getRoll();
pitch = dataCollector.getPitch();
yaw = dataCollector.getYaw();
Point p = new Point();
p.setLocation(Math.abs(pitch) * 10, Math.abs(yaw) * 10);
setPoint(p);
repaint();
}
}
};
}
What I would like to happen is for a red circle to be drawn somewhere on the GUI depending on the orientation of the external device. At this point, my "test print statement" doesn't fire even once.
My guess is that I'm lacking some sort of basic understanding of Java's GlassPane or even how paint, paintComponent, and repaint even works. Could anyone point out what I'm doing wrong?

The likely cause of your frustration is trying to set the glass pane visible (Swing components are visible by default), before setting it as the frames GlassPane.
The JFrame is likely resetting the glass pane to be invisible, meaning that it won't be painted (no point painting something that's not visible)
Try setting the glass pane visible AFTER you apply it to the frame

I am trying to move a ball in applet using thread but its not moving

I am trying to move a ball in applet using thread but its not moving. Can anyone help me out as m new to applet and proceeding for game development..for reference here is my code
public class ballGame extends JApplet implements Runnable
{
int x_pos=50;
int y_pos=100;
int rad=10;
Thread t;
public void start()
{
super.start();
t=new Thread("t");
t.start();
}
public void paint(Graphics g)
{
super.paint(g);
g.setColor(Color.red);
setBackground(Color.BLACK);
g.drawOval(x_pos,y_pos,2*rad,2*rad);
while(true)
{
x_pos++;
//validate();
repaint();
try
{
Thread.sleep(100);
}
catch(Exception e)
{
e.printStackTrace();
}
}//end of while
}//end of paint()
}

Swing is a single thread environment. That is, all updates and interactions are executed within a single thread. Swing is also NOT thread safe. This means that all updates to the UI MUST be executed within the context of that thread (the Event Dispatching Thread or ETD).
Any code that blocks the EDT will prevent it from (amongst other things), repainting the UI and responding to input from the user.
You're paint code will NEVER update the screen, in fact it will make your application appear to "hang", as the paint method isn't being allowed to complete and is blocking the ETD.
It is an exception that the paint method will return quickly after been called and may be called repeatedly in quick succession.
Generally speaking, a Thread is probably a little over kill, something like a javax.swing.Timer would be more then suitable under these circumstances.
public class AnimatedBoat {
public static void main(String[] args) {
new AnimatedBoat();
}
public AnimatedBoat() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
}
JFrame frame = new JFrame("Test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new AnimationPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class AnimationPane extends JPanel {
private BufferedImage boat;
private int xPos = 0;
private int direction = 1;
public AnimationPane() {
try {
boat = ImageIO.read(new File("boat.png"));
Timer timer = new Timer(40, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
xPos += direction;
if (xPos + boat.getWidth() > getWidth()) {
xPos = getWidth() - boat.getWidth();
direction *= -1;
} else if (xPos < 0) {
xPos = 0;
direction *= -1;
}
repaint();
}
});
timer.setRepeats(true);
timer.setCoalesce(true);
timer.start();
} catch (IOException ex) {
ex.printStackTrace();
}
}
#Override
public Dimension getPreferredSize() {
return boat == null ? super.getPreferredSize() : new Dimension(boat.getWidth() * 4, boat.getHeight());
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
int y = getHeight() - boat.getHeight();
g.drawImage(boat, xPos, y, this);
}
}
}
As a side note. You should rarely need to override the paint method of a top level container like JApplet or JFrame, while there are a number of good reasons for this, the one that you're going to most interested in is the fact that they're not double buffered, meaning you are likely to see flickering as the screen is updated.
It's better to use something like JPanel and override it's paintComponent method instead.
Take a look at
Performing Custom Painting
Concurrency in Swing
Painting in AWT and Swing
For more information
nb
While I've used a JFrame for my example, it would be a simple matter to take the animation panel and put it into a JApplet, this is another reasons why you don't need/want to extend from top level containers ;)

Having an infinite loop in paint means that not a single pass of the method can complete.
Also you should never call Thread.sleep(100) in the paint method. This blocks the EDT and degrades performance.
Instead use a Swing Timer to do the update and repainting work. Also I would sub-class a JComponent and override paintComponent.

You can not invoke repaint() method inside paint(). And you can not organize infinitely loop inside paint() method - doing so, you are blocking drawing in your applet.

x_posis an int value, thus it is passed to methods by value, not by reference. That is why, when you change its value, the value inside of your circle is not updated...

You create a Thread without a run() method. This method should contain the runnable code... Furthermore, the paint() method is to paint stuff, not update stuff!
So move your while loop from the paint() method into the run() method of your thread:
t=new Thread("t") {
#Override
public void run()
{
while(true)
{
x_pos++;
//validate();
repaint();
try
{
Thread.sleep(100);
}
catch(Exception e)
{
e.printStackTrace();
}
}//end of while
}
};
Note that ballGame does not require the implement Runnable part. As the thread you created will provide it.

Have the while loop inside the run method of Runnable.
UPDATE:
Have this in the start method.
t=new Thread(this);
t.start();

Visual Artifacts appearing on JPanel

I am trying to create a program with 2 JPanel using BorderLayout. The center panel is for random drawing of rectangle while the south panel is for the buttons.
I am getting a weird image of the button on the top left corner of the JFrame whenever I hover the mouse cursor over the North or South button. I did some research and found out that this could be the reason for having a transparent background. I tried using super.paintComponent(g) for the panel but the rest of the rectangles drawn earlier disappear. I need the rectangles to stay in the JPanel but not the weird image on the top left.
I don't know what I am doing wrong, hopefully someone can help or give some clue on how to solve this problem.
public class TwoBRandomRec extends JFrame{
private static final long serialVersionUID = 1L;
public static void main(String[] args) {
TwoBRandomRec rec = new TwoBRandomRec();
rec.setSize(500,500);
rec.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
rec.setVisible(true);
}
public TwoBRandomRec() {
//Create the buttons
JButton north = new JButton("North");
JButton south = new JButton("South");
DrawPanel drawPanel = new DrawPanel(500,500);
JPanel southP = new JPanel();
southP.add(south);
southP.add(north);
this.add(drawPanel, BorderLayout.CENTER);
this.add(southP, BorderLayout.SOUTH);
this.setTitle("TwoButtonRandomRec");
this.pack();
}
public class DrawPanel extends JPanel {
private static final long serialVersionUID = 1L;
private Random rand = new Random();
private int x,y,xSize,ySize;
private int height,width;
public DrawPanel(int w,int h) {
width = w;
height = h;
}
public void RandomX(){
x=rand.nextInt(width-1);
xSize=rand.nextInt(width-x);
}
public void RandomY(){
y=rand.nextInt(height-1);
ySize=rand.nextInt(height-y);
}
public Color RandomColour(){
rand.nextInt(height);
return new Color(rand.nextInt(255),rand.nextInt(255),rand.nextInt(255));
}
#Override
protected void paintComponent(Graphics g) {
RandomX();
RandomY();
g.setColor(RandomColour());
g.fillRect(x, y, xSize, ySize);
try {
Thread.sleep(50);
} catch (InterruptedException e) {
}
repaint();
}
}
}

You're not calling super.paintComponent
protected void paintComponent(Graphics g) {
super.paintComponent(g); // <-- Insert me here and watch problem go away
RandomX();
RandomY();
g.setColor(RandomColour());
g.fillRect(x, y, xSize, ySize);
try {
Thread.sleep(50); // <-- This is an INCREDIBLY bad idea, NEVER, EVER do this
} catch (InterruptedException e) {
}
repaint(); // <-- This is a bad idea, watch CPU max out...
}
You are obligated to call super.paintComponent to ensure that the paint chain is upheld correctly and things like opacity and cleaning up of the graphics context takes place.
The Graphics object is shared between components through a single repaint pass, failure to honor the correct paint chain will result in, well, problems like yours
Never update the UI in anyway from any paint method (this includes calling repaint), this is just causing your paint method to be recalled, over and over and over...until you CPU hits 100% and program hangs.
Never, EVER do any time consuming or block operations within the paint methods (or the UI generally), this will make it look like the program as hung and make the users upset (you think zombi hordes are bad :P). Blocking in this way prevents the EDT from responding to paint requests...
I'd recommend having a read through:
Performing Custom Painting
2D Graphics
Painting in AWT and Swing
Concurrency in Swing

Added BufferedImage is only 2x2 pixels

I have a script that cycles (almost like a slideshow) through a Vector object (flipBook), using a Thread (animationThread), and adds them to a JPanel. However, the added image is only 2x2 pixels large.
I've verified the images are 50x50, but they don't appear to be properly showing.
Here's some of the code going on behind the Thread instance. I'm not entirely sure which code would be beneficial for finding the source for.
public void startThread() {
if (flipWidth != 0 && flipHeight != 0) {
System.out.println("[ AnimationAsset ] " + "We're starting the thread");
Runnable r = new Runnable() {
#Override
public void run() {
runWork();
}
};
animationThread = new Thread(r, "AnimationThread");
animationThread.start();
going = true;
}
}
private void runWork() {
try {
while (going) {
repaint();
flipIndex = (flipIndex + 1) % numFlips;
System.out.println("[ AnimationAsset ] flipIndex: " + flipIndex);
Thread.sleep(1000);
}
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
System.out.println("[ AnimationAsset ] " + "Interrupted");
}
}
public void paint(Graphics g) {
update(g);
}
public void update(Graphics g) {
System.out.println("[ AnimationAsset ] " + flipIndex);
((Graphics2D) g).drawImage(flipBook.get(flipIndex), null, 5, 5);
}

and adds them to a JPanel
This is not a Swing code. This is AWT code.
You would never override the update() and paint() methods this way when using Swing. Get rid of this code and start over.
To do this in Swing I would use a JLabel with an Icon and add the label to the frame.
Then, to do animation in SWing your should use a Swing Timer.
When the timer fires you simply use the setIcon(...) method of the label to replace the old icon with your new icon.

Emm you have a strange drawing code as
((Graphics2D) g).drawImage(flipBook.get(flipIndex), null, 5, 5);
You can see the docs here... to use Graphic2D drawImage() method right
the most common way of image drawing is to paint image right on JComponent, as a rule, the JLabel. Here is a component example
public class MyLabel extends JLabel
{
private Image image;
public MyLabel(Image image)
{
this.image=image;
}
public void paintComponent(Graphics g)
{
g.drawImage(this.image,x,y,width,height,null);
}
}
so here you can use the component as a common swing object
public class MyPanel extends JPanel
{
public MyPanel()
{
Image image=null;
try{
image=ImageIO.read(new File("image.png"));
}
catch (IOException e) {
}
this.add(new MyLabel(image));
}
}
Good luck