Develop Reference

Repaint doesn't work when changing variable

I am very new to developing with java but I have some general coding experience. I know wanted to draw a "picture/fractal" with a function I created. I got all the code done and I wanted to automatically move the "fractal" by just adding to the function XOFF, (I have a timer) now I wanted the variable to automatically increase so that it scrolls through the picture. I tried using repaint and revalidate but it doesnt work :(
and i know that i wrote MandelBrotSet even though it doesn't have anything to do with it ^^
package Pack1;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import javax.swing.Timer;
import javax.swing.JComponent;
import javax.swing.JFrame;
public class Main extends JComponent implements ActionListener {
public static void main(String[] args) {
new Main();
}
public static final int WIDTH = 1000;
public static final int HEIGHT = 800;
public int XOFF = 0;
public int YOFF = 0;
private BufferedImage buffer;
private Timer timer;
public Main(){
buffer = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
timer = new Timer(10, this);
renderMandelBrotSet();
JFrame frame = new JFrame("Mandelbrot Set");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setResizable(true);
frame.getContentPane().add(this);
frame.pack();
frame.setVisible(true);
}
#Override
public void addNotify() {
setPreferredSize(new Dimension(WIDTH, HEIGHT));
timer.start();
}
public void renderMandelBrotSet() {
System.out.println(XOFF);
int vx = 0;
int vy = 0;
int zoom = 1;
for(int x = 0; x < WIDTH; x++)
for(int y = 0; y < HEIGHT; y++) {
vx = ((x - WIDTH/2));
vy = ((y - HEIGHT/2));
vx = vx + XOFF;
vy = vy + 0;
int color = (int) (Math.abs(vx)/Math.sqrt(Math.abs(vy))*(vx/zoom)); //calculatePoint((x - WIDTH/2), (y - HEIGHT/2) );
buffer.setRGB(x, y, color);
}
}
#Override
public void paint(Graphics g) {
g.drawImage(buffer, 0, 0, null);
}
#Override
public void actionPerformed(ActionEvent e) {
XOFF++;
renderMandelBrotSet();
revalidate();
repaint();
}
}
I hope the code makes sense..., I am sorry if I forgot to mention anything. Feel free to ask me if you need something.

I think addNotify is your problem. That method already does something, and the way you overrode it you don't seem to perform any of the actions that its documentation says it should. Just get rid of it, and move its code elsewhere.
This seems to work for me. I also slowed your timer down to 100 ms since I know from experience that Java Swing isn't really capable of updating as quickly as that. 100 ms to 250 ms is a good range for updating Swing.
I also got rid of revalidate because that's only for when a component is added or removed, or changes size. You only need to repaint since your image doesn't change size.
(Hovercraft pointed out that the code really should override paintComponent, not paint. He is quite correct; this is explained in the tutorial: https://docs.oracle.com/javase/tutorial/uiswing/painting/closer.html )
(And while I'm fixing stuff up I might as well point out that Swing is not thread safe, and the GUI creation (including the image and the timer) really needs to be done on the GUI thread.)
package quicktest;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.Timer;
/**
*
* #author Brenden
*/
public class MandelbrotSet {
}
class Main extends JComponent implements ActionListener {
public static void main(String[] args) {
new Main();
}
public static final int WIDTH = 800;
public static final int HEIGHT = 600;
public int XOFF = 0;
public int YOFF = 0;
private BufferedImage buffer;
private Timer timer;
public Main(){
SwingUtilities.invokeLater( this::createGui );
}
private void createGui() {
buffer = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
timer = new Timer(100, this);
setPreferredSize( new Dimension( WIDTH, HEIGHT ) );
renderMandelBrotSet();
JFrame frame = new JFrame("Mandelbrot Set");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setResizable(true);
frame.getContentPane().add(this);
frame.pack();
frame.setVisible(true);
timer.start();
}
// #Override
// public void addNotify() {
// setPreferredSize(new Dimension(WIDTH, HEIGHT));
// timer.start();
// }
public void renderMandelBrotSet() {
System.out.println(XOFF);
int vx = 0;
int vy = 0;
int zoom = 1;
for(int x = 0; x < WIDTH; x++)
for(int y = 0; y < HEIGHT; y++) {
vx = ((x - WIDTH/2));
vy = ((y - HEIGHT/2));
vx = vx + XOFF;
vy = vy + 0;
int color = (int) (Math.abs(vx)/Math.sqrt(Math.abs(vy))*(vx/zoom)); //calculatePoint((x - WIDTH/2), (y - HEIGHT/2) );
buffer.setRGB(x, y, color);
}
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent( g );
System.err.println( "Repainting..." );
g.drawImage(buffer, 0, 0, null);
}
#Override
public void actionPerformed(ActionEvent e) {
System.err.println( "Timer: XOFF=" + XOFF );
XOFF++;
renderMandelBrotSet();
// revalidate();
repaint();
}
}

Rescale a drawing in Java (JFrame)

I need the simplest way to rescale a drawing in java (for example a rectangle...). I found a way to "stretch" them:
import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JFrame;
import java.awt.Dimension;
public class Stretch extends JFrame {
int originalHeight = 600;
int originalWidth = 600;
public Stretch() {
super("Stretch");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setSize(originalWidth, originalHeight);
}
public static void main(String[] args) {
Stretch s = new Stretch();
s.setVisible(true);
}
public void paint(Graphics g) {
Dimension size = this.getBounds().getSize();
int rectWidth = 100;
int rectHeight = 130;
g.setColor(Color.white);
g.fillRect(0, 0, size.width, size.height);
g.setColor(Color.black);
g.drawRect(100, 100, rectWidth + size.width - originalWidth, rectHeight + size.height - originalHeight);
}
}
As you can see the formula is like that:
g.drawRect(100, 100, rectWidth + size.width - originalWidth, rectHeight + size.height - originalHeight);
Now how can I rescale the drawing? Width and height have to maintain the same proportion.
Thank you.

There are bascially two different approaches for this:
You can "scale the whole Graphics"
You can scale the actual shapes
The difference may be subtle in some cases, but can be important: When you scale the whole Graphics, then everything will be scaled. Particularly, when you scale it about 2.0, and then draw a line with a width of 1.0, the line will be drawn 2 pixels wide. Whether or not this is desired depends on the application case.
In order to scale the actual shapes, you can not use the drawRect method. Instead you will have to create Shape instances that represent the geometric shapes. You can then create scaled versions of these shapes with AffineTransform#createTransformedShape.
Here is an example that compares both approaches (and corrects some of the other issues that have been in your code). In both cases, the same rectangle with an original size of (10,13) is painted, scaled by a factor of 5.0.
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Shape;
import java.awt.geom.AffineTransform;
import java.awt.geom.Rectangle2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class ScalingDrawnObjects
{
public static void main(String[] args)
{
SwingUtilities.invokeLater(new Runnable()
{
#Override
public void run()
{
createAndShowGUI();
}
});
}
private static void createAndShowGUI()
{
JFrame f = new JFrame();
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
ScalingDrawnObjectsPanel p = new ScalingDrawnObjectsPanel();
f.getContentPane().add(p);
f.setSize(600,400);
f.setLocationRelativeTo(null);
f.setVisible(true);
}
}
class ScalingDrawnObjectsPanel extends JPanel
{
#Override
protected void paintComponent(Graphics gr)
{
super.paintComponent(gr);
Graphics2D g = (Graphics2D)gr;
Shape rectangle = new Rectangle2D.Double(2, 2, 10, 13);
g.setColor(Color.RED);
drawWithScaledGraphics(g, rectangle);
g.translate(100, 0);
drawScaledObject(g, rectangle);
}
private static void drawWithScaledGraphics(Graphics2D g, Shape shape)
{
AffineTransform oldAt = g.getTransform();
g.scale(5.0, 5.0);
g.draw(shape);
g.setTransform(oldAt);
}
private static void drawScaledObject(Graphics2D g, Shape shape)
{
AffineTransform at = AffineTransform.getScaleInstance(5.0, 5.0);
g.draw(at.createTransformedShape(shape));
}
}
EDIT In response to the comment
The code that I posted is not "complicated". It is as compilcated as it has to be, but not more. You should not extend JFrame and you should not override paint. You should create the GUI on the EDT. You should ...
However, you should not use code like the following, but maybe this is what you're looking for
import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JFrame;
import java.awt.Dimension;
public class Stretch extends JFrame {
int originalHeight = 600;
int originalWidth = 600;
public Stretch() {
super("Stretch");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setSize(originalWidth, originalHeight);
}
public static void main(String[] args) {
Stretch s = new Stretch();
s.setVisible(true);
}
public void paint(Graphics g) {
Dimension size = this.getBounds().getSize();
int rectWidth = 100;
int rectHeight = 130;
g.setColor(Color.white);
g.fillRect(0, 0, size.width, size.height);
g.setColor(Color.black);
int w = rectWidth + size.width - originalWidth;
int h = rectHeight + size.height - originalHeight;
double sx = (double)w / rectWidth;
double sy = (double)h / rectHeight;
double s = Math.min(sx, sy);
int fw = (int)(s * rectWidth);
int fh = (int)(s * rectHeight);
g.drawRect(100, 100, fw, fh);
}
}

How about multiplying the width and the height by the scale you want?
So if you want to scale it by 2:
g.drawRect(100, 100, 2 * (rectWidth + size.width - originalWidth), 2 * (rectHeight + size.height - originalHeight));

How to paint a circle with a random size on a random coordinate such that the circle is fully visible?

Code:
Random rand = new Random();
JPanel mainPanel;
int randomSize = 0;
int randomPositionX = 0;
int randomPositionY = 0;
final static int FRAME_HEIGHT = 500;
final static int FRAME_WIDTH = 500;
final static int TITLE_BAR = 30 ;
final static int MAX_SIZE = 100;
final static int MIN_SIZE = 10 ;
/* All the below code is put into a method */
mainPanel = new JPanel(){
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.RED);
g.fillOval(randomPositionY, randomPositionX, randomSize, randomSize);
}
};
do{
randomSize = rand.nextInt(MAX_SIZE) + 1;
}while(randomSize < MIN_SIZE);
do{
randomPositionX = rand.nextInt(FRAME_WIDTH);
randomPositionY = rand.nextInt(FRAME_HEIGHT);
}while((randomPositionX + randomSize > FRAME_WIDTH) || (randomPositionY + randomSize > FRAME_HEIGHT - TITLE_BAR));
repaint();
What I want is the circle to have a random size such that it should have a minimum size of 10 and a maximum size of 100. The circle should also be painted in a random coordinate such that the circle is fully visible inside the JPanel mainPanel.
Note that mainPanel will be added to a JFrame whose size is set using setSize(FRAME_WIDTH, FRAME_HEIGHT);.
But the problem is that sometimes, a part of the circle is half outside and half inside the JPanel:
Where did I go wrong?

You're trying to use the frame size when calculating the position of the circle, when the frame includes a variable high title bar AND frame insets
You're trying to use the frame size when it's irrelevant, it's the component's size you should be using, as it's within the mainPanel's coordinate context which you want to paint
So, how do I fix the issues?
Discard ALL the frame "padding"/"offsets". The mainPanel has it's own coordinate context (it's top left corner will be 0x0) and it will be within it's parent's coordinate context, so you don't need to care about the frame or it's insets.
Simplify your calculations, for example...
int randomSize = MIN_SIZE + (rand.nextInt(MAX_SIZE) + 1);
int randomPositionX = rand.nextInt(getWidth() - randomSize);
int randomPositionY = rand.nextInt(getHeight() - randomSize);
Should allow you to produce results which won't fall outside of the viewable area, as the maximum range of the dimensions is the current size of the container minus the desired size, just beware, if the available size is smaller then MAX_SIZE, you will have issues ;)
The example generates a new circle every second
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.util.Random;
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();
}
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public static class TestPane extends JPanel {
public final static int MAX_SIZE = 100;
public final static int MIN_SIZE = 10;
private Rectangle bounds;
private Random rand;
public TestPane() {
rand = new Random();
Timer timer = new Timer(1000, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
int randomSize = MIN_SIZE + (rand.nextInt(MAX_SIZE) + 1);
int randomPositionX = rand.nextInt(getWidth() - randomSize);
int randomPositionY = rand.nextInt(getHeight() - randomSize);
bounds = new Rectangle(randomPositionX, randomPositionY, randomSize, randomSize);
repaint();
}
});
timer.start();
}
#Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
if (bounds != null) {
g2d.setColor(Color.RED);
g2d.fillOval(bounds.x, bounds.y, bounds.width, bounds.height);
}
g2d.dispose();
}
}
}

Repaint in Panel method not updated

I am trying to make a program that work like this:
In Window class every time I click on the button, the method panel2 of Panel is called: first it is drawing a first circle, then a second one (after the time defined in the timer). Then, I click again on the button, and it is drawing a fist circle, then a second one then a third one. etc.
The problem is that it when I click to obtain 3 circles appearing one after the other, the two first circles drawn at the previous step (before I pressed a second time the button) stay on the screen and only the third circle is drawn when i press the button (instead of having : first circle drawn, second circle drawn, third circle drawn). I hope I am clear.
Here is a simple code:
Window
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Window extends JFrame implements ActionListener{
int h = 2;
Panel b = new Panel();
JPanel container = new JPanel();
JButton btn = new JButton("Start");
JButton bouton = new JButton();
Panel boutonPane = new Panel();
public Window(){
this.setTitle("Animation");
this.setSize(300, 300);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setLocationRelativeTo(null);
container.setBackground(Color.white);
container.setLayout(new BorderLayout());
JPanel top = new JPanel();
btn.addActionListener(this);
top.add(btn);
container.add(top);
this.setContentPane(container);
this.setVisible(true);
}
public void window2(){
this.setTitle("ADHD");
this.setSize(1000,700);
this.setLocationRelativeTo(null);
if (h < 11){
boutonPane.panel2(h);
bouton.addActionListener(this);
boutonPane.add(bouton);
this.add(boutonPane);
this.setContentPane(boutonPane);
updateWindow2();
}
this.setVisible(true);
}
public void updateWindow2(){
boutonPane.panel2(h);
this.revalidate();
this.repaint();
}
public void actionPerformed(ActionEvent e){
if ((JButton) e.getSource() == btn){
System.out.println("pressed0");
window2();
}
if ((JButton) e.getSource() == bouton){
h++;
System.out.println("pressed" + h);
updateWindow2();
}
}
public static void main(String[] args){
Window w = new Window();
}
}
Panel
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JPanel;
import javax.swing.Timer;
public class Panel extends JPanel implements ActionListener{
int m;
int u=0;
int lgi, lrgi;
int [] ta;
Timer timer1 = new Timer(300, this);
Panel(){
}
public void panel2(int n){
m=n;
ta = new int [n];
for(int it=0; it<m;it++){
ta[it]=100*it;
}
timer1.start();
}
public void paintComponent(Graphics gr){
super.paintComponent(gr);
gr.setColor(Color.red);
for(int i=0;i<m;i++){
gr.fillOval(ta[i],ta[i], 150, 150);
}
}
#Override
public void actionPerformed(ActionEvent arg0) {
if(u<m){
u++;
revalidate();
repaint();
}
}
}

Your code needs use two int values to decide how many circles to draw and when:
The first int should be the count of current circles to draw, say called, currentCirclesToDraw.
The second int will be the number of circles to draw total.
If you use a List<Ellipse2D> like I suggest, then this number will be the size of the list. So if the List is called ellipseList, then the 2nd number will be ellipseList.size().
The first variable will be incremented in the timer up to the size of the list, but no larger, and will be used by paintComponent method to decide how many circles to draw.
Key point here: the first number, the currentCirclesToDraw, must be re-set to 0 when the button is pressed. This way your paintComponent method will start out drawing 0 circles, then 1, then 2, ...
For example, the paintComponent method could look like so:
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g2.setColor(CIRCLE_COLOR);
for (int i = 0; i < currentCirclesToDraw && i < ellipseList.size(); i++) {
g2.fill(ellipseList.get(i));
}
}
I use the second term in the for loop conditional statement, i < currentCirclesToDraw && i < ellipseList.size() as an additional fail-safe to be sure that we don't try to draw more circles then we have in our list.
My Timer's ActionListener would increment the currentCirclesToDraw variable and call repaint. It would stop the Timer once currentCirclesToDraw reaches the size of the ellipseList:
private class TimerListener implements ActionListener {
#Override
public void actionPerformed(ActionEvent e) {
if (currentCirclesToDraw < ellipseList.size()) {
currentCirclesToDraw++;
repaint();
} else {
// stop the Timer
((Timer)e.getSource()).stop();
}
}
}
And my button's actionPerformed method would reset currentCirclesToDraw to 0, would add a new Ellipse2D to my ellipseList (if we've not yet reached the MAX_CIRCLE_INDEX), would call repaint() to clear the JPanel, and would construct and start the Timer:
public void actionPerformed(java.awt.event.ActionEvent arg0) {
currentCirclesToDraw = 0; // this is key -- reset the index used to control how many circles to draw
if (ellipseList.size() < MAX_CIRCLE_INDEX) {
double x = (ellipseList.size()) * CIRCLE_WIDTH / Math.pow(2, 0.5);
double y = x;
double w = CIRCLE_WIDTH;
double h = CIRCLE_WIDTH;
ellipseList.add(new Ellipse2D.Double(x, y, w, h));
}
repaint(); // clear image
new Timer(TIMER_DELAY, new TimerListener()).start();
};
Edit 3/30/14
Note it all can be put together like this:
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.geom.Ellipse2D;
import java.util.ArrayList;
import java.util.List;
import javax.swing.*;
/**
* http://stackoverflow.com/a/22714405/522444
* http://stackoverflow.com/questions/22712655/repaint-in-panel-method-not-updated
* #author Pete
*
*/
#SuppressWarnings("serial")
public class TimerCircles extends JPanel {
private static final int PREF_W = 1000;
private static final int PREF_H = 700;
private static final Color CIRCLE_COLOR = Color.RED;
public static final int MAX_CIRCLE_INDEX = 11;
public static final int TIMER_DELAY = 300;
public static final int CIRCLE_WIDTH = 100;
private final List<Ellipse2D> ellipseList = new ArrayList<>();
private int currentCirclesToDraw = 0;
public TimerCircles() {
add(new JButton(new ButtonAction("New Circle", KeyEvent.VK_C)));
}
#Override
public Dimension getPreferredSize() {
return new Dimension(PREF_W, PREF_H);
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g2.setColor(CIRCLE_COLOR);
for (int i = 0; i < currentCirclesToDraw && i < ellipseList.size(); i++) {
g2.fill(ellipseList.get(i));
}
}
private class ButtonAction extends AbstractAction {
public ButtonAction(String name, int mnemonic) {
super(name);
putValue(MNEMONIC_KEY, mnemonic);
}
public void actionPerformed(java.awt.event.ActionEvent arg0) {
currentCirclesToDraw = 0; // this is key -- reset the index used to control how many circles to draw
if (ellipseList.size() < MAX_CIRCLE_INDEX) {
double x = (ellipseList.size()) * CIRCLE_WIDTH / Math.pow(2, 0.5);
double y = x;
double w = CIRCLE_WIDTH;
double h = CIRCLE_WIDTH;
ellipseList.add(new Ellipse2D.Double(x, y, w, h));
}
repaint(); // clear image
new Timer(TIMER_DELAY, new TimerListener()).start();
};
}
private class TimerListener implements ActionListener {
#Override
public void actionPerformed(ActionEvent e) {
if (currentCirclesToDraw < ellipseList.size()) {
currentCirclesToDraw++;
repaint();
} else {
// stop the Timer
((Timer)e.getSource()).stop();
}
}
}
private static void createAndShowGui() {
TimerCircles mainPanel = new TimerCircles();
JFrame frame = new JFrame("TimerCircles");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}

"Infinite" Loop with Timer

I was wondering if anybody here knows how to make a seamlessly endless loop with shapes using a timer. Basically I'm trying to make a new set of moving shapes while the current set of shapes is moving so that it looks like it's just infinitely moving along the top of the screen. I have tried the if statements alongside the public int getX(){return x;)}, but I have not succeeded in doing so. Maybe it's possible to have a second timer linked with a second set of shapes and set a delay time? (However, I do not know how to go about writing a second timer and I do not know how to set a delay, help me??)
Any solutions or suggestions?
Here is an example, notice how the set of shapes is redrawn after all of the shapes pass the screen. This is not what I want. I want it to appear as if it were infinitely running along the top of the screen in smooth succession.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class ExampleLoop extends JPanel implements ActionListener {
public static void main(String[] args) {
JFrame frame = new JFrame();
frame.setSize(500, 500);
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new ExampleLoop());
frame.setVisible(true);
}
Timer timer = new Timer(50, this);
int x = 0, velX = 7;
// CHRISTMAS THEME :D
public void paintComponent(Graphics g) {
g.setColor(Color.RED);
g.fillRect(0, 0, 500, 500);
g.setColor(Color.GREEN);
for (int z = 0; z <= 500; z += 100)
g.fillRect(x + z, 0, 20, 20);
timer.start();
}
public void actionPerformed(ActionEvent e) {
if (x < 500) {
velX = velX;
x = x + velX;
}
else {
x = 0;
}
repaint();
}
}

I can't really figure out what going on in your code, but I reproduce the effect you're looking for. You can examine it. It runs.
What i did was make 5 different xPoints. You could have done this by using an array of int but I thouhgt it would be easier to read this way.
For each xPoint, I incremented each timer iteration. If the xPoint reached the screen width, I made it equal 0. Then repaint. I did that for all the points.
Code Edited: to use arrays and loops
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
public class GreenRects extends JPanel {
private static final int SCREEN_WIDTH = 500;
private static final int SCREEN_HEIGHT = 500;
private static final int OFFSET = 100;
private static final int SIZE = 20;
private static final int INC = 5;
int[] xPoints = new int[5];
public GreenRects() {
int x = 0;
for (int i = 0; i < xPoints.length; i++) {
xPoints[i] = x;
x += OFFSET;
}
Timer timer = new Timer(50, new ActionListener() {
public void actionPerformed(ActionEvent e) {
for (int i = 0; i < xPoints.length; i++) {
if (xPoints[i] + INC < SCREEN_WIDTH) {
xPoints[i] += INC;
} else {
xPoints[i] = 0;
}
}
repaint();
}
});
timer.start();
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.red);
g.fillRect(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT);
g.setColor(Color.green);
for (int i = 0; i < xPoints.length; i++) {
g.fillRect(xPoints[i], 0, SIZE, SIZE);
}
}
public Dimension getPreferredSize() {
return new Dimension(SCREEN_WIDTH, SCREEN_HEIGHT);
}
public static void createAndShowGui() {
JFrame frame = new JFrame();
frame.add(new GreenRects());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLocationRelativeTo(null);
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}

You can try this code in if clause
if (x < 80)
{
velX = velX;
x = x + velX;
}