Develop Reference

Java drawing a circle using awt,JFrame with Thread(Runnable) on Netbeans (Mac)

https://github.com/terryaa/KOSTA_MAC/tree/master/Java/NetBeans/day13_01_15/src/ex1
What I'm trying to do is to draw circles, but one circle on a canvas at a time and then moving on to drawing next circle using Runnable join. It should draw a circle using .start() and the other .start() shouldn't start until formal .start()'s drawing circle is done.
In linked page's package, Ex3_Canvas1 class has main and use Runnable MyThread0 class to draw a circle using basic .start() and .join() and it does perfectly what I want.
I created NetBean's automatic JFrame class Ex2_CanvasDemo and tried to do the same and failed. JFrame window pops up after drawing a full circle and then shows creating of next circle. What I want is that the window should first appear and it shows creation of both circles ,not simulataneously but sequently, like Ex3_Canvas1.
I guess it's because main thread waits for th(Ex2_CanvasDemo) to finish so window doesn't apply for changes. But shouldn't Ex1_Canvas1 should do the same? Is this differences due to automatically generated code by netbeans? How can I do the same as Ex1_Canvas1 in Ex2_CanvasDemo.
I tried making a Runnable class and used in Ex2_CanvasDemo but failed also..
Any help?
I'm using jdk 8 and netbeans8 on mac.
--Thread part of Ex2_CanvasDemo--
public Ex2_CanvasDemo() {
initComponents();
Thread th=new Thread(new Runnable() {
#Override
public void run() {
for(int i=0;i<370;i+=10){
try {
Thread.sleep(100);
} catch (InterruptedException ex) {
Logger.getLogger(Ex2_CanvasDemo.class.getName()).log(Level.SEVERE, null, ex);
}
arcNUm=i;
System.out.println("circle"+arcNUm);
canvas1.repaint();
}
}
});
th.start();
try {
th.join();
} catch (InterruptedException ex) {
Logger.getLogger(Ex2_CanvasDemo.class.getName()).log(Level.SEVERE, null, ex);
}
th=new Thread(new Runnable() {
#Override
public void run() {
for(int i=0;i<370;i+=10){
System.out.println("circle"+i);
try {
Thread.sleep(100);
} catch (InterruptedException ex) {
Logger.getLogger(Ex2_CanvasDemo.class.getName()).log(Level.SEVERE, null, ex);
}
arcNum2=i;
canvas2.repaint();
}
}
});
th.start();
// try {
// th.join();
// } catch (InterruptedException ex) {
// Logger.getLogger(Ex2_CanvasDemo.class.getName()).log(Level.SEVERE, null, ex);
// }
}

Caveat
Animation is hard, good animation is really hard. You need to repeat this to yourself, because animation done right is, really hard.
What you need to know...
Animation is basically the illusion of change over time. Very rarely do you want to perform linear animation, animation is normally done over a period of time, as it allows for performance difference in the platform to be smoothed out in away which is not as harsh to the user.
Swing is single threaded and not thread safe. This means that you should not block the event dispatching thread and that you must only update the UI from within the context of the event dispatching thread.
See Concurrency in Swing for more details
This makes life a little difficult, as you can't simply run a linear loop in the EDT, as this will block the UI and it's difficult to do it from a Thread because it's a mess of synchronisation.
One of the simplest solutions is to make use of the available API and use a Swing Timer, which acts as a pseudo loop, putting in a small delay between call backs, in which you can perform some operations
Example...
While there are a number of ways you might approach this, I've set up a simple List which contains a bunch of Animatables which "do stuff" and then simply run one after the other in serial.
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.Ellipse2D;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class Test {
public static void main(String[] args) {
new Test();
}
public Test() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
ex.printStackTrace();
}
TestPane testPane = new TestPane();
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(testPane);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
testPane.play();
}
});
}
});
}
public class TestPane extends JPanel {
private List<Animatable> animations;
private Animatable animation;
private Timer timer;
public TestPane() {
animations = new ArrayList<>(25);
animations.add(new CircleAnimation(Color.RED));
animations.add(new CircleAnimation(Color.BLUE));
timer = new Timer(5, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
if (animation == null) {
animation = animations.remove(0);
}
if (animation.update(getBounds())) {
if (animations.isEmpty()) {
((Timer)e.getSource()).stop();
} else {
animation = animations.remove(0);
}
}
repaint();
}
});
}
public void play() {
timer.start();
}
#Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (animation != null) {
Graphics2D g2d = (Graphics2D) g.create();
animation.paint(g2d);
g2d.dispose();
}
}
}
public interface Animatable {
public boolean update(Rectangle bounds);
public void paint(Graphics2D g2d);
}
public class CircleAnimation implements Animatable {
private Color color;
private Ellipse2D circle;
private double delta = -1;
public CircleAnimation(Color color) {
this.color = color;
}
#Override
public boolean update(Rectangle bounds) {
if (circle == null) {
circle = new Ellipse2D.Double(bounds.width, (bounds.height / 2) - 10, 20, 20);
}
Rectangle rect = circle.getBounds();
rect.x += delta;
circle.setFrame(rect);
return rect.x + 20 < bounds.x;
}
#Override
public void paint(Graphics2D g2d) {
if (circle == null) {
return;
}
g2d.setColor(color);
g2d.fill(circle);
}
}
}

Java repaint() method doesn't always work

There is a problem with the repaint() method in Java. I made a new thread that constantly repaints the screen. When I release the spacebar I want my player to fall smoothly by setting its position and then waiting for 50 milliseconds and looping that 20 times. Instead, it waits the whole amount of time in the loop, then repaints. I am wondering why it doesn't constantly repaint the changes in the players co-ordinates. Thank you.
(Edit) Thanks everyone for the help. This is my first time using stack overflow, and I am only 13 and still learning java, so I probably will go back to the tutorials again.
My 'a' class (main):
public class a {
public static void main(String[] args) {
JFrame frame = new JFrame("StickFigure Game");
frame.setSize(740, 580);
frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
b board = new b();
frame.add(board);
frame.addKeyListener(board);
}
}
My 'b' class (JPanel/drawing):
public class b extends JPanel implements KeyListener {
c player = new c();
public class MyRunnable implements Runnable {
public void run() {
while (true)
repaint();
}
}
MyRunnable run = new MyRunnable();
public void paint(Graphics g) {
super.paint(g);
Graphics2D g2d = (Graphics2D) g;
g2d.drawImage(player.getImage(), player.getX(), player.getY(), 80, 140,
null);
}
public b() {
Thread thread = new Thread(new MyRunnable());
thread.start();
}
public static void slow(int n) {
long t0, t1;
t0 = System.currentTimeMillis();
do {
t1 = System.currentTimeMillis();
} while (t1 - t0 < n);
}
public void keyPressed(KeyEvent e) {
if (e.getKeyCode() == KeyEvent.VK_D) {
player.setPos(player.getX() + 6, player.getY());
}
if (e.getKeyCode() == KeyEvent.VK_A) {
player.setPos(player.getX() - 6, player.getY());
}
if (e.getKeyCode() == KeyEvent.VK_SPACE) {
player.setPos(player.getX(), player.getY() - 60);
}
}
public void keyReleased(KeyEvent e) {
if (e.getKeyCode() == KeyEvent.VK_SPACE) {
for (int i = 0; i < 20; i++) {
slow(50);
player.setPos(player.getX(), player.getY() + 2);
}
}
}
public void keyTyped(KeyEvent e) {
}
}
my 'c' class (player):
public class c {
private ImageIcon i = new ImageIcon("guy.png");
private Image img = i.getImage();
private int x = 0;
private int y = 100;
public void wait(int what) {
try {
Thread.sleep(what);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public c() {
}
public Image getImage() {
return img;
}
public int getX() {
return x;
}
public int getY() {
return y;
}
public void setPos(int mx, int my) {
x = mx;
y = my;
}
}

I haven't gone through all the code here but here are some pointers:
Swing has its own concurrency mechanisms which allow you to handle UI updates. You can use a Swing Timer rather than a raw Thread. Related is the use of Thread.sleep - don't do this, it only blocks the EDT and prevents UI updates.
The Swing paint chain mechanism requires you to override paintComponent rather than paint.
Always use Key Bindings rather than KeyListeners in Swing. KeyListeners require component focus to work to interact with the KeyEvents. Key Bindings do not have this limitation.

"There is a problem with the repaint() method in java." Did you consider that perhaps the problem is with your code instead? You are blocking the event thread and giving the system no time to do the intermediate repaints. In particular, this method:
public static void slow (int n){
long t0,t1;
t0=System.currentTimeMillis();
do{
t1=System.currentTimeMillis();
}
while (t1-t0<n);
}
and this loop:
for(int i = 0;i<20;i++){
slow(50);
player.setPos(player.getX(), player.getY()+2);
}
do not relinquish control to the system so that repaints can actually happen. Rewrite those using Swing timers. Look at this tutorial for an introduction on how to use these.
Also, your thread that constantly calls repaint() in a tight loop:
public void run(){
while(true) repaint();
}
is a terrible idea. You don't need to call repaint() at full CPU speed. Once every 30 milliseconds or so is fine for animation. Again, consider using Swing utilities to do this rather than writing your own looping thread.

The repaint is only a "request" to paint as soon as possible. so when you call it it causes a call to the paint method as soon as possible.
from here
So basically you just flooding the scheduled calls of paint or update with while(true) repaint();.
Oracle's stance on painting in AWT and Swing
One way you could do it, or should I say how I would do it, is to make your c class implement KeyListener, so that when a key is pressed (and only when it is pressed) you update it's location.
So move your KeyListener methods to class c, in your class b constructor you can add the call this.addKeyListener(player) or make a method void addPlayer(c player) that adds it.

Strange Error in Java ME

I've just starting delving into the wonders of Java ME but have become frustrated when trying to create a thread...
Below is the code which compiles absolutely fine. However, as soon as I install it on my G600 and run it, 'Java Game Error' pops up.
My method of putting it in a jar file and installing it works, as I have created a game with no threads and that works fine.
import java.util.Random;
import javax.microedition.lcdui.*;
import javax.microedition.lcdui.game.*;
import javax.microedition.midlet.*;
public class CanvasTest extends MIDlet {
Display display;
public CanvasTest() {
}
public void startApp() {
TestCanvas thecanvas = new TestCanvas();
display = Display.getDisplay(this);
display.setCurrent(thecanvas);
}
public void pauseApp() {}
public void destroyApp(boolean unconditional) {}
}
class TestCanvas extends GameCanvas implements Runnable {
Font font;
int width;
int height;
boolean running = true;
public TestCanvas() {
super(false);
setFullScreenMode(true);
width = getWidth();
height = getHeight();
Thread thisThread = new Thread(this);
thisThread.start();
}
public void paint(Graphics g) {
Random rand = new Random();
g.setColor(rand.nextInt(255), rand.nextInt(255), rand.nextInt(255));
g.fillRect(0, 0, width, height);
}
public void run() {
while(running) {
paint(getGraphics());
flushGraphics();
try {
Thread.sleep(50);
}
catch(InterruptedException ex) {}
}
}
};
Note: yes, this is not the game, it merely demonstrates the problem I am facing.
Thanks in advance!

Just a wild guess, but a general rule in Java is that you can't "touch" the UI out of the main thread. Well, this a little bit roughly explained, but there are many articles about the topic.
I suggest you to avoid calling UI methods like paint() or flushGraphics() from a separate Thread.
I hope it helps.

did you test it at emulator prior to phone? if not - why? if yes - how did it go?
regarding the code it looks OK to me except for the slippery two lines where you create and start thread from constructor. I'd rather move these two lines at the end of startApp
public void startApp() {
TestCanvas theCanvas= new TestCanvas();
display = Display.getDisplay(this);
display.setCurrent(theCanvas);
new Thread(theCanvas).start(); // add here and...
}
//...
public TestCanvas() {
super(false);
setFullScreenMode(true);
width = getWidth();
height = getHeight();
// ...and remove here
// Thread thisThread = new Thread(this);
// thisThread.start();
}

Java Applet Game Loop stops Mouse/Keyboard Input?

I got a problem I couldn't get to work after about 2 Hours of trying. I want to have a loop that do 2 Methods (Draw and update) but also listen to Mouse/Keyboard events. I have a loop that Draws and Updates, but does nothing outside of the loop ( Listening to events ) I tried alot of things but nothing worked. Help Please?
I tried using the Runnable Thread, using different orders, using wait() and notify(), I've tried alot of things. But basicly I want to know how to run a loop and still check for User Input
Also when I try to quit the program clicking the red "X", it won't quit but still work
Here's the Code:
import java.applet.Applet;
import java.awt.*;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
public class main extends Applet implements MouseListener, Runnable {
public main() {
super();
init();
}
Thread t;
Screen screen = new Screen();
String Text = "Hello";
boolean Running = true;
boolean Click = false;
int R = 0x00;
int G = 0x00;
int B = 0x00;
int xpoints[] = {25, 40, 40, 25, 25};
int ypoints[] = {40, 40, 25, 25, 25};
int npoints = 5;
public void run() {
while (Running) {
GameLoop();
}
}
public void init() {
this.addMouseListener(this);
this.setSize(400, 300); //manually set your Frame's size
t = new Thread(this);
t.start();
}
public void paint(Graphics g) {
g.setColor(new Color(R, B, G));
g.fillPolygon(xpoints, ypoints, npoints);
Running = true;
t.run();
}
public void mousePressed(MouseEvent e) { //On Mouse Click
System.exit(0);
}
public void mouseReleased(MouseEvent e) {
}
public void mouseEntered(MouseEvent e) {
System.exit(0);
}
public void mouseExited(MouseEvent e) {
}
public void mouseClicked(MouseEvent e) {
}
public boolean keyDown(Event e, int key) {
return true;
}
public void GameLoop() {
if (Running) {
if (R != 0xff) {
R++;
} else {
if (G != 0xff) {
G++;
} else {
if (B != 0xff) {
B++;
} else {
System.exit(0);
}
}
}
try {
sleep(20);
} catch (InterruptedException e) {
e.printStackTrace();
}
paint(getGraphics());
}
}
public void sleep(int time) throws InterruptedException {
Thread.sleep(time, 0);
}
}

This tutorial should provide some insight as to how your program should be structured. And this one is helpful for the mouse listener.
Issues you should address:
1) You're doing something fishy with the paint method. Why are you calling t.run() in there? The thread t is already running and looping constantly calling the paint() method to redraw the screen. Remove this call and see what you get.
1) The destruction of your thread/applciation is poor. The first example above provides a better way for that to occur
2) You have your System.Exit(0) on mousePressed() with the comment //on mouse click but nothing in mouseClicked()... it works but its bad convention
3)Having your class named main is extremely poor convention that is both confusing and impractical. Rename your class to something like "Game" or similar.
4) Why declare Screen if you don't use it?

I see that you define a Running variable to be true upon initialization. This variable is used to determine whether or not the game should stop. I, however, don't see any place where you modify the value of this variable to false. This would explain why your game never exits.
As for the the game not working, try debugging the application in an IDE. You should then pay attention to what, if any, Exception are being thrown and the values of any variables you are questioning. Hopefully this will give you insight into the behavior of your app.
Don't forget to update us with any new info you discover so we can help you out along the way.

Issue with Java join() method

First of all here are some code snippets:
public void startThread() {
this.animationThread = new Thread(this);
this.animationThread.start();
try {
this.animationThread.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
#Override
public void run() {
pirateMainAnimation.animate();
}
public void animate() {
for (int j = 0; j < 9; j++) {
try {
Thread.sleep(250);
} catch (InterruptedException e) {
break;
}
PirateAnimationPanel.getInstance().setCurrent(j);
PirateAnimationPanel.getInstance().repaint();
}
}
I'm trying to animate some images. The thing is that I want the main thread to wait for the animation thread to finish and then to continue. I searched around, read a little bit and decided to use the join() method. It perfectly waits for the thread to finish but I doesn't animate correctly. The repaint() method gets called 2 times instead of nine. I think maybe the problem is because I used singletons. Here is the singleton implementation.
import java.awt.Graphics;
import java.awt.MediaTracker;
import javax.swing.JPanel;
import uk.ac.aber.dcs.piratehangman.animation.PirateMainAnimation;
import uk.ac.aber.dcs.piratehangman.utilityclasses.AnimationThread;
#SuppressWarnings("serial")
public class PirateAnimationPanel extends JPanel {
private int current;
private MediaTracker mTracker;
private PirateMainAnimation pirateMainAnimation;
private AnimationThread animationThread;
private PirateAnimationPanel() {
this.current = 0;
this.pirateMainAnimation = new PirateMainAnimation();
mTracker = new MediaTracker(this);
this.animationThread = new AnimationThread();
setMediaTracker();
repaint();
}
private void setMediaTracker() {
for (int i = 0; i < 9; i++) {
mTracker.addImage(
this.pirateMainAnimation.getImagesForAnimation()[i],
this.pirateMainAnimation.getImagesForAnimationID()[i]);
try {
mTracker.waitForID(this.pirateMainAnimation
.getImagesForAnimationID()[i]);
} catch (InterruptedException e) {
System.out.println("Error loading image: " + i);
}
}
}
public void playAnimation() {
this.animationThread.startThread();
}
public void paintComponent(Graphics g) {
super.paintComponents(g);
System.out.println("called");
g.drawImage(this.pirateMainAnimation.getImagesForAnimation()[current],
0, 0, this);
}
private static class PirateAnimationPanelHolder {
private static final PirateAnimationPanel pirateAnimationPanel =
new PirateAnimationPanel();
};
public static PirateAnimationPanel getInstance() {
return PirateAnimationPanelHolder.pirateAnimationPanel;
}
public void setCurrent(int current) {
this.current = current;
}
public int getCurrent() {
return current;
}
}

I think you mean that the paintComponent() methods only gets called twice. Also I think you should be able to remove the call to super.paintComponents() if you fill the component to the background color.
The repaint() method only marks the component as dirty and requests a re-render on the next paint.
I would have expected the Swing thread to be able to repaint within the 250ms but I'm not sure what other work is being done/rendered. You might want to put a call to MediaTracker.waitForAll() before the animation.
While the static singleton is not adding much I don't think it is causing a problem (in this case).
Update:
So the problem is that the join() is on the Swing event Thread which is blocking the repainting of the component. I suggested a call like the following to show the "new game dialog after the last animation:
SwingUtilities.invokeLater(new Runnable() {
public void run() { showDialog(); }
})

"Note that events being posted to the EventQueue can be coalesced," which may explain the disparity. Also, be certain to build your GUI on event dispatch thread. See A More Complex Image Icon Example for a more detailed discussion.
Addendum: Improving Perceived Performance When Loading Image Icons has a nice SwingWorker example that may simplify the off-loading.