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Why is my code in Swing just returning a black screen? [duplicate]

I'm creating a graphical front-end for a JBox2D simulation. The simulation runs incrementally, and in between the updates, the contents of the simulation are supposed to be drawn. Similar to a game except without input.
I only need geometric primitives to draw a JBox2D simulation. This API seemed like the simplest choice, but its design is a bit confusing.
Currently I have one class called Window extending JFrame, that contains as a member another class called Renderer. The Window class only initializes itself and provides an updateDisplay() method (that is called by the main loop), that calls updateDisplay(objects) method on the Renderer. I made these two methods myself and their only purpose is to call repaint() on the Renderer.
Is the JPanel supposed to be used that way? Or am I supposed to use some more sophisticated method for animation (such that involves events and/or time intervals in some back-end thread)?

If you are wanting to schedule the updates at a set interval, javax.swing.Timer provides a Swing-integrated service for it. Timer runs its task on the EDT periodically, without having an explicit loop. (An explicit loop would block the EDT from processing events, which would freeze the UI. I explained this more in-depth here.)
Ultimately doing any kind of painting in Swing you'll still be doing two things:
Overriding paintComponent to do your drawing.
Calling repaint as-needed to request that your drawing be made visible. (Swing normally only repaints when it's needed, for example when some other program's window passes over top of a Swing component.)
If you're doing those two things you're probably doing it right. Swing doesn't really have a high-level API for animation. It's designed primarily with drawing GUI components in mind. It can certainly do some good stuff, but you will have to write a component mostly from scratch, like you're doing.
Painting in AWT and Swing covers some of the 'behind the scenes' stuff if you do not have it bookmarked.
You might look in to JavaFX. I don't know that much about it personally, but it's supposed to be more geared towards animation.
As somewhat of an optimization, one thing that can be done is to paint on a separate image and then paint the image on to the panel in paintComponent. This is especially useful if the painting is long: repaints can be scheduled by the system so this keeps when it happens more under control.
If you aren't drawing to an image, then you'd need to build a model with objects, and paint all of them every time inside paintComponent.
Here's an example of drawing to an image:
import javax.swing.*;
import java.awt.*;
import java.awt.image.*;
import java.awt.event.*;
/**
* Holding left-click draws, and
* right-clicking cycles the color.
*/
class PaintAnyTime {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new PaintAnyTime();
}
});
}
Color[] colors = {Color.red, Color.blue, Color.black};
int currentColor = 0;
BufferedImage img = new BufferedImage(256, 256, BufferedImage.TYPE_INT_ARGB);
Graphics2D imgG2 = img.createGraphics();
JFrame frame = new JFrame("Paint Any Time");
JPanel panel = new JPanel() {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
// Creating a copy of the Graphics
// so any reconfiguration we do on
// it doesn't interfere with what
// Swing is doing.
Graphics2D g2 = (Graphics2D) g.create();
// Drawing the image.
int w = img.getWidth();
int h = img.getHeight();
g2.drawImage(img, 0, 0, w, h, null);
// Drawing a swatch.
Color color = colors[currentColor];
g2.setColor(color);
g2.fillRect(0, 0, 16, 16);
g2.setColor(Color.black);
g2.drawRect(-1, -1, 17, 17);
// At the end, we dispose the
// Graphics copy we've created
g2.dispose();
}
#Override
public Dimension getPreferredSize() {
return new Dimension(img.getWidth(), img.getHeight());
}
};
MouseAdapter drawer = new MouseAdapter() {
boolean rButtonDown;
Point prev;
#Override
public void mousePressed(MouseEvent e) {
if (SwingUtilities.isLeftMouseButton(e)) {
prev = e.getPoint();
}
if (SwingUtilities.isRightMouseButton(e) && !rButtonDown) {
// (This just behaves a little better
// than using the mouseClicked event.)
rButtonDown = true;
currentColor = (currentColor + 1) % colors.length;
panel.repaint();
}
}
#Override
public void mouseDragged(MouseEvent e) {
if (prev != null) {
Point next = e.getPoint();
Color color = colors[currentColor];
// We can safely paint to the
// image any time we want to.
imgG2.setColor(color);
imgG2.drawLine(prev.x, prev.y, next.x, next.y);
// We just need to repaint the
// panel to make sure the
// changes are visible
// immediately.
panel.repaint();
prev = next;
}
}
#Override
public void mouseReleased(MouseEvent e) {
if (SwingUtilities.isLeftMouseButton(e)) {
prev = null;
}
if (SwingUtilities.isRightMouseButton(e)) {
rButtonDown = false;
}
}
};
PaintAnyTime() {
// RenderingHints let you specify
// options such as antialiasing.
imgG2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
imgG2.setStroke(new BasicStroke(3));
//
panel.setBackground(Color.white);
panel.addMouseListener(drawer);
panel.addMouseMotionListener(drawer);
Cursor cursor =
Cursor.getPredefinedCursor(Cursor.CROSSHAIR_CURSOR);
panel.setCursor(cursor);
frame.setContentPane(panel);
frame.pack();
frame.setResizable(false);
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
If the routine is long-running and repaints could happen concurrently, double buffering can also be used. Drawing is done to an image which is separate from the one being shown. Then, when the drawing routine is done, the image references are swapped so the update is seamless.
You should typically use double buffering for a game, for example. Double buffering prevents the image from being shown in a partial state. This could happen if, for example, you were using a background thread for the game loop (instead of a Timer) and a repaint happened the game was doing the painting. Without double buffering, this kind of situation would result in flickering or tearing.
Swing components are double buffered by default, so if all of your drawing is happening on the EDT you don't need to write double buffering logic yourself. Swing already does it.
Here is a somewhat more complicated example which shows a long-running task and a buffer swap:
import java.awt.*;
import javax.swing.*;
import java.awt.image.*;
import java.awt.event.*;
import java.util.*;
/**
* Left-click to spawn a new background
* painting task.
*/
class DoubleBuffer {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new DoubleBuffer();
}
});
}
final int width = 640;
final int height = 480;
BufferedImage createCompatibleImage() {
GraphicsConfiguration gc =
GraphicsEnvironment
.getLocalGraphicsEnvironment()
.getDefaultScreenDevice()
.getDefaultConfiguration();
// createCompatibleImage creates an image that is
// optimized for the display device.
// See http://docs.oracle.com/javase/8/docs/api/java/awt/GraphicsConfiguration.html#createCompatibleImage-int-int-int-
return gc.createCompatibleImage(width, height, Transparency.TRANSLUCENT);
}
// The front image is the one which is
// displayed in the panel.
BufferedImage front = createCompatibleImage();
// The back image is the one that gets
// painted to.
BufferedImage back = createCompatibleImage();
boolean isPainting = false;
final JFrame frame = new JFrame("Double Buffer");
final JPanel panel = new JPanel() {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
// Scaling the image to fit the panel.
Dimension actualSize = getSize();
int w = actualSize.width;
int h = actualSize.height;
g.drawImage(front, 0, 0, w, h, null);
}
};
final MouseAdapter onClick = new MouseAdapter() {
#Override
public void mousePressed(MouseEvent e) {
if (!isPainting) {
isPainting = true;
new PaintTask(e.getPoint()).execute();
}
}
};
DoubleBuffer() {
panel.setPreferredSize(new Dimension(width, height));
panel.setBackground(Color.WHITE);
panel.addMouseListener(onClick);
frame.setContentPane(panel);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
void swap() {
BufferedImage temp = front;
front = back;
back = temp;
}
class PaintTask extends SwingWorker<Void, Void> {
final Point pt;
PaintTask(Point pt) {
this.pt = pt;
}
#Override
public Void doInBackground() {
Random rand = new Random();
synchronized(DoubleBuffer.this) {
Graphics2D g2 = back.createGraphics();
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g2.setRenderingHint(RenderingHints.KEY_STROKE_CONTROL,
RenderingHints.VALUE_STROKE_PURE);
g2.setBackground(new Color(0, true));
g2.clearRect(0, 0, width, height);
// (This computes pow(2, rand.nextInt(3) + 7).)
int depth = 1 << ( rand.nextInt(3) + 7 );
float hue = rand.nextInt(depth);
int radius = 1;
int c;
// This loop just draws concentric circles,
// starting from the inside and extending
// outwards until it hits the outside of
// the image.
do {
int rgb = Color.HSBtoRGB(hue / depth, 1, 1);
g2.setColor(new Color(rgb));
int x = pt.x - radius;
int y = pt.y - radius;
int d = radius * 2;
g2.drawOval(x, y, d, d);
++radius;
++hue;
c = (int) (radius * Math.cos(Math.PI / 4));
} while (
(0 <= pt.x - c) || (pt.x + c < width)
|| (0 <= pt.y - c) || (pt.y + c < height)
);
g2.dispose();
back.flush();
return (Void) null;
}
}
#Override
public void done() {
// done() is completed on the EDT,
// so for this small program, this
// is the only place where synchronization
// is necessary.
// paintComponent will see the swap
// happen the next time it is called.
synchronized(DoubleBuffer.this) {
swap();
}
isPainting = false;
panel.repaint();
}
}
}
The painting routine is just intended draw garbage which takes a long time:

For a tightly coupled simulation, javax.swing.Timer is a good choice. Let the timer's listener invoke your implementation of paintComponent(), as shown here and in the example cited here.
For a loosely coupled simulation, let the model evolve in the background thread of a SwingWorker, as shown here. Invoke publish() when apropos to you simulation.
The choice is dictated in part by the nature of the simulation and the duty cycle of the model.

Why not just use stuff from the testbed? It already does everything. Just take the JPanel, controller, and debug draw. It uses Java 2D drawing.
See here for the JPanel that does the buffered rendering:
https://github.com/dmurph/jbox2d/blob/master/jbox2d-testbed/src/main/java/org/jbox2d/testbed/framework/j2d/TestPanelJ2D.java
and here for the debug draw:
https://github.com/dmurph/jbox2d/blob/master/jbox2d-testbed/src/main/java/org/jbox2d/testbed/framework/j2d/DebugDrawJ2D.java
See the TestbedMain.java file to see how the normal testbed is launched, and rip out what you don't need :)
Edits:
Disclaimer: I maintain jbox2d
Here is the package for the testbed framework: https://github.com/dmurph/jbox2d/tree/master/jbox2d-testbed/src/main/java/org/jbox2d/testbed/framework
TestbedMain.java is in the j2d folder, here:
https://github.com/dmurph/jbox2d/tree/master/jbox2d-testbed/src/main/java/org/jbox2d/testbed/framework/j2d

Java Thread : I want to fade in and out the image but when I compile the image is not shown

This is my code please help and explain what I did wrong thank you very much.
Also I am a bit confuse about Thread whether I did correctly way.
public class Fade extends JPanel implements Runnable {
static Image image;
private float alpha = 0f;
static JFrame frame;
public static void main(String[] args) throws IOException {
image = new ImageIcon(ImageIO.read(new File("gummybear.jpg")))
.getImage();
frame = new JFrame("fade frame");
frame.add(new Fade());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(image.getWidth(frame), image.getHeight(frame));
// set picture in the center of screen
frame.setLocationRelativeTo(null);
frame.setVisible(true);
ExecutorService executor = Executors.newFixedThreadPool(1);
Runnable fade = new Fade();
executor.execute(fade);
// executor.shutdown();
// while (!executor.isTerminated()) {
// }
// System.out.println("Finished fade in / fade out threads");
}
public void run() {
while (alpha < 1) {
try {
System.out.println(alpha);
alpha += 0.1f;
this.repaint();
Thread.sleep(100);
} catch (InterruptedException ex) {
Logger.getLogger(Fader.class.getName()).log(Level.SEVERE, null,
ex);
}
}
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
// SRC_OVER: If pixels in the source and the destination overlap, only
// the source
// pixels outside of the overlapping area are rendered. The pixels in
// the overlapping area are not changed.
g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER,
alpha));
g2d.drawImage(image, 0, 0, null);
// Color c = new Color(255, 255, 255, alpha);
// g2d.setColor(c);
// g2d.fillRect(0, 0, image.getWidth(frame), image.getHeight(frame));
System.out.println("repaint");
}
}
...............

Image Stuff
It looks to me that you want to add transparency to an image that was loaded from a JPG file. JPG files don't have an alpha channel (that is used for transparency), so this will not work.
You find a good example for working with transparency (and loading images from JPG) in the one of the Java tutorials: Drawing an Image
There you find a nice example with code that does nearly what you want: change the transparency of an image loaded from a JPG file. The difference is that the opacity value is taken from a slider control instead of a timed variable.
Threading Stuff
Edit: I just realized, that you are using Swing, an API that is not designed to be thread safe.
I just have to point you to the Java Tutorials How to Use Swing Timers and Concurrency in Swing then.

The problem is that you are not changing the alpha value. At least, not the alpha value of the Fade instance that you are showing:
// Here you are adding a "Fade" instance to the frame.
frame.add(new Fade());
...
// Here you are creating a NEW "Fade" instance. Only in
// this instance, the alpha value will be affected
Runnable fade = new Fade();
executor.execute(fade);
Change this to
// Create a Fade instance and add it to the frame
Fade fade = new Fade();
frame.add(fade);
...
// Submit the SAME Fade instance to the executor
executor.execute(fade);
You'll also have to verify that the alpha value remains in [0,1], but this can be done with something like
alpha += 0.1f;
alpha = Math.min(1.0f, alpha);

Why isn't anything getting drawn to my awt window on the second call to paint?

I have the following code that draws an invisible window on the entire screen:
Window w=new Window(null)
{
private int x = 200; private int y=200;
private int dx = 2; private int dy = 2;
private final int CIRCLE_DIAMETER = 400;
#Override
public void paint(Graphics g)
{
g.setColor(Color.ORANGE);
g.fillOval(x, y, CIRCLE_DIAMETER, CIRCLE_DIAMETER);
}
#Override
public void update(Graphics g)
{
if(x<=0)
dx*=-1;
if(y<=0)
dy*=-1;
if(x+CIRCLE_DIAMETER>=this.getWidth())
dx*=-1;
if(y+CIRCLE_DIAMETER>=this.getHeight())
dy*=-1;
x+=dx;
y+=dy;
this.paint(g);
}
};
w.setAlwaysOnTop(true);
w.setBounds(w.getGraphicsConfiguration().getBounds());
w.setBackground(new Color(0, true));
w.setVisible(true);
//Lazy way of making calls to paint for testing
while(true){
w.repaint();
try {
Thread.sleep(100);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
This draws an orange circle on the screen at the coordinates x and y. When I call repaint in my infinite loop, paint gets called and the x and y get updated, but the circle never gets drawn in another position. If I print the values of x and y to every call of paint they are getting updated properly, so I do not know why it isn't getting drawn. Does anyone know what I am doing wrong here?
Thanks for any suggestions!

I am new here so I may be wrong.
I think that your problem is something to do with how you are using a Window object and not a JPanel. So change your Window object to a JPanel. You should probably close that up with a JFrame in order to complete the final window.
You should be using a JPanel I think so that the methods that you can use to perform the drawing of the ball to move are implemented properly.
Instead of overriding the paint() method you need to override the paintComponent() method.
Following the cycle of drawing your objects.
Like so...
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.ORANGE);
g.fillOval(x, y, CIRCLE_DIAMETER, CIRCLE_DIAMETER);
}
The super.paintComponent() should empty the original image out of the JPanel and you should then be able to draw your updated image.
These may help you as well(I haven't really looked at them properly):
Java ball moving
http://docs.oracle.com/javase/tutorial/uiswing/painting/
Java Bouncing Ball
Sorry if I missed something. (I haven't tested your code)

How to tell when Graphics.drawImage() has actually completed

This is my first time asking a question on here, and I'm hoping I get an answer or an idea that will help me.
I am drawing a large image and scaling it down with drawImage(). I then immediately draw another image with drawImage() that I expect to be drawn on top of the previous one (second). The problem is that drawImage returns immediately, even if it takes ~50 ms to scale and render the first image. Most of the time the second image ends up underneath the first one because it's painted first while the big first one is being processed. Basically is there anyway to force drawImage() to block until it's done, or to somehow check when it has completed?
I'm aware of the ImageObserver parameter, which works fine when downloading an image from the Internet or something, but when using an already-loaded BufferedImage, it never fires ImageUpdate() just after scaling and drawing. Basically since the first image is already "loaded" it never contacts the ImageObserver, it just takes like ~50 ms in it's own thread to process, never notifying when it completes.
Does anyone know how to either force it to block or wait until it's completely done scaling and blitting an image? And obviously using Thread.sleep(xx) is a complete hack and not viable due to differences between computer speeds. All this rendering is happened on the Event thread inside the paint(Graphics g) method.
Thanks!
EDIT: The following is code I currently have to give you an idea of the issue:
public void paint(Graphics window)
{
window.setColor(Color.WHITE);
window.fillRect(0, 0, Settings.width * Settings.aaFactor, Settings.height * Settings.aaFactor);
Graphics2D window2D = (Graphics2D) window;
window2D.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BICUBIC);
window2D.drawImage(this.image, 0, 0, Settings.width, Settings.height, null);
try
{
Thread.sleep(50);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
window2D.drawImage(this.image2, 0, 0, null);
repaint();
}
EDIT 2: To better explain the problem I'm talking about, I made some sample code that does better what I'm trying to explain. Run it and you will see it flickering where sometimes the first image is on bottom (like it's supposed to be), but most of the time it will be one top (second), which is wrong. Just change the File paths to a small image and a large image.
public class Main extends Applet implements ImageObserver
{
private BufferedImage imageA;
private BufferedImage imageB;
#Override
public void init()
{
try
{
this.imageA = ImageIO.read(new File("C:\\LargeImage.jpg"));
this.imageB = ImageIO.read(new File("C:\\SmallImage.jpg"));
}
catch (IOException e)
{
e.printStackTrace();
}
}
#Override
public void update(Graphics g)
{
paint(g);
}
#Override
public void paint(Graphics g)
{
Graphics2D w = (Graphics2D) g;
w.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BICUBIC);
w.drawImage(this.imageA, 0, 0, 50, 50, this);// This takes a while to do (scaling down and drawing)...
w.drawImage(this.imageB, 10, 10, null);// While this is drawn quickly, before A is done.
repaint();
}
#Override
public boolean imageUpdate(Image img, int infoflags, int x, int y, int width, int height)
{
System.out.println("ImageObserver fired, done drawing image. NEVER CALLED!");
return false;
}
}

The last argument to drawImage (where you pass null) is an ImageObserver. If you provide your own implementation of that interface (see JavaDoc), you will be informed when the image has been actually drawn.

It is impossible to know when Swing will actually render the contents of a Graphics object to the screen. What is know is it won't happen until AFTER the paint methods return (as the Graphics object hasn't been finalised for rendering until it does).
What you should do is let the Component you are painting to make the decision as to when something needs to updated, this is the way it was designed...(Component implements ImageObserver)
The below example continuously re-scales the master background image as the frame is resized
public class TestPaint03 {
public static void main(String[] args) {
new TestPaint03();
}
public TestPaint03() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (Exception ex) {
}
JFrame frame = new JFrame("Test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new PaintPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class PaintPane extends JPanel {
private BufferedImage background;
private BufferedImage foreground;
private Image scaled;
public PaintPane() {
try {
background = ImageIO.read(new File("/path/to/background/image));
foreground = ImageIO.read(new File("path/to/foreground/image"));
} catch (Exception e) {
}
}
#Override
public void invalidate() {
scaled = null;
super.invalidate();
}
#Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (background != null) {
if (scaled == null) {
int size = Math.min(getWidth(), getHeight());
scaled = background.getScaledInstance(-1, size, Image.SCALE_SMOOTH);
}
int x = (getWidth() - scaled.getWidth(this)) / 2;
int y = (getHeight() - scaled.getHeight(this)) / 2;
g.drawImage(scaled, x, y, this);
x = (getWidth() - foreground.getWidth()) / 2;
y = (getHeight() - foreground.getHeight()) / 2;
g.drawImage(foreground, x, y, this);
}
}
}
}
While I'm sure you have your reasons, personally I would avoid Applet in favor of JApplet and in fact, I would personally avoid applets or together. I started my career coding applets, they are simply a pain, especially when all you're trying to do is test an idea.

How to get rid of the flicker that appears during my animation?

I'm learning Java by making a small game in a JApplet.
I got a little problem with my sprite's animation.
Here is the code :
this.sprite.setBounds(0,0,20,17);
this.sprite.setIcon(this.rangerDown);
for(int i = 0; i< 16;i++)
{
this.sprite.setBounds(this.sprite.getX(), this.sprite.getY()+1, 20, 17);
this.sprite.update(this.sprite.getGraphics());
try{
Thread.currentThread().sleep(100);
}catch(InterruptedException e){
}
}
It left some flicker during the animation. Once the animation end, the flicker disappears, but it's kind of ugly... I guess there is some step I missed.
I use this method because it gives the better result for now, but I would like to stay without AWT if possible, using Swing instead.
Any ideas how to get rid of the flicker?
Thanks for reading.
Screenshoot (Can't post images, sorry).

This is not a shadow. Its the border of your sprite. It just happens to be black and appears as a shadow. If you change the amount you shift your sprite (lets say by 50 pixels, not just 1) you will see what i mean.
To fix it what you need to do is to draw the background as well each time you update the location of your sprite. Although this will probably produce flickering.
The correct way to do it is to change the way you draw your objects. You need to override the paintComponent method of your panel and then simply call repaint each time you have updated the locations of your sprites.
EDIT:
See this code sample for basic usage. NOTE: This is NOT how you should write animation using Threads. I wrote that to show you what goes in the paintComponent method and wrote the animation Thread to show you that the "shadow" you mentioned is gone. NEVER have a non ending run loop in a thread :)
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Test {
public static void main(String[] args) {
JFrame f = new JFrame("Test");
MyPanel c = new MyPanel();
f.getContentPane().add(c);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setSize(350, 100);
f.setVisible(true);
}
}
class MyPanel extends JPanel {
int x = 0;
boolean toTheRight = true;
public MyPanel() {
new Thread(new Runnable() {
#Override
public void run() {
while (true) {
x = (toTheRight)?x+5:x-5;
if (x>300)
toTheRight = false;
if (x<0)
toTheRight = true;
repaint();
try {
Thread.sleep(50);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}).start();
}
#Override
protected void paintComponent(Graphics g) {
Graphics2D g2 = (Graphics2D)g.create();
g2.setPaint(Color.white);
g2.fillRect(0, 0, getWidth(), getHeight());
g2.setPaint(Color.red);
g2.fillOval(x-2, 50, 4, 4);
}
}

The problem is double buffering.
In Applets:
Double buffering is done almost automatically. Call repaint() instead of paint in your method.
In Swing, there are many ways to do it. I usually go for the BufferStrategy route. When you're initializing your frame, do this:
JFrame frame;
... code to init frame here
frame.createBufferStrategy(2);
Then in your draw methods:
Graphics g = getBufferStrategy().getDrawGraphics();
..code to do drawing here...
g.dispose();
getBufferStrategy().show();