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java gui paintComponent refresh

I am learning java gui interface and wrote a program that has a button. Each time the button is clicked, a random sized rectangle will be added to the screen. But instead of adding it to the screen, the program keeps erasing the old one, which I want to keep on the screen. Here is my code. I tried to do paint() and it did not work. Thanks in advance.
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
public class SimpleGui implements ActionListener {
JFrame frame = new JFrame();
public static void main(String[] args){
SimpleGui gui = new SimpleGui();
gui.go();
}
public void go(){
JButton button = new JButton("Add a rectangle");
MyDrawPanel panel = new MyDrawPanel();
button.addActionListener(this);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(BorderLayout.SOUTH, button);
frame.getContentPane().add(BorderLayout.CENTER, panel);
frame.setSize(300, 300);
frame.setVisible(true);
}
public void actionPerformed(ActionEvent event){
frame.repaint();
}
class MyDrawPanel extends JPanel{
public void paintComponent(Graphics g){
g.setColor(Color.blue);
int height = (int) (Math.random()*120 + 10);
int width = (int) (Math.random()*120 + 10);
int x = (int) (Math.random()*40 + 10);
int y = (int) (Math.random()*40 + 10);
g.fillRect(x, y, height, width);
}
}
}

Your paintComponent method is written to draw only one rectangle, so its behavior should come as no shock to you. If you want it to draw multiple, you have one of two options:
Create an ArrayList<Rectangle>, and in the actionPerformed method, add a new random Rectangle to this List and then call repaint(). In the paintComponent method, iterate through this List with a for-loop, painting each Rectangle.
Or you could draw the new random rectangle onto a BufferedImage that is displayed by the paintComponent method.
The first method is the easier of the two, the 2nd is better if you're worried about program responsiveness, say in an animation program.
For example:
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.image.BufferedImage;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import javax.swing.*;
#SuppressWarnings("serial")
public class TwoDrawRectMethods extends JPanel {
// Array to hold our two drawing JPanels
private AddRandomRect[] addRandomRects = {
new DrawList("Using List"),
new DrawBufferedImage("Using BufferedImage")};
// constructor
public TwoDrawRectMethods() {
// add drawing rectangles onto GUI
for (AddRandomRect addRandomRect : addRandomRects) {
add(addRandomRect);
}
// button to tell rectangles to add a new Rectangle
add(new JButton(new DrawAction("Add New Rectangle")));
}
// The button's Action -- an ActionListener on "steroids"
private class DrawAction extends AbstractAction {
public DrawAction(String name) {
super(name);
int mnemonic = (int) name.charAt(0);
putValue(MNEMONIC_KEY, mnemonic);
}
#Override
public void actionPerformed(ActionEvent e) {
// tell both drawing JPanels to add a new rectangle
for (AddRandomRect addRandomRect : addRandomRects) {
addRandomRect.addRectangle();
}
}
}
private static void createAndShowGui() {
TwoDrawRectMethods mainPanel = new TwoDrawRectMethods();
JFrame frame = new JFrame("TwoDrawRectMethods");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(() -> createAndShowGui());
}
}
#SuppressWarnings("serial")
class DrawList extends AddRandomRect {
private static final Color RECT_COLOR = Color.RED;
private List<Rectangle> rectList = new ArrayList<>();
public DrawList(String title) {
super(title);
}
#Override
public void addRectangle() {
rectList.add(createRandomRect());
repaint();
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setColor(RECT_COLOR);
for (Rectangle rectangle : rectList) {
g2.draw(rectangle);
}
}
}
#SuppressWarnings("serial")
class DrawBufferedImage extends AddRandomRect {
private static final Color RECT_COLOR = Color.BLUE;
private BufferedImage img = null;
public DrawBufferedImage(String title) {
super(title);
}
#Override
public void addRectangle() {
if (img == null) {
img = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_ARGB);
}
Rectangle rect = createRandomRect();
Graphics2D g2 = img.createGraphics();
g2.setColor(RECT_COLOR);
g2.draw(rect);
g2.dispose();
repaint();
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (img != null) {
g.drawImage(img, 0, 0, null);
}
}
}
#SuppressWarnings("serial")
abstract class AddRandomRect extends JPanel {
private static final int PREF_W = 500;
private static final int PREF_H = PREF_W;
private Random random = new Random();
public AddRandomRect(String title) {
setBorder(BorderFactory.createTitledBorder(title));
}
abstract void addRectangle();
protected Rectangle createRandomRect() {
int x1 = random.nextInt(PREF_W);
int x2 = random.nextInt(PREF_W);
int y1 = random.nextInt(PREF_H);
int y2 = random.nextInt(PREF_H);
int x = Math.min(x1, x2);
int y = Math.min(y1, y2);
int width = Math.abs(x1 - x2);
int height = Math.abs(y1 - y2);
return new Rectangle(x, y, width, height);
}
#Override
public Dimension getPreferredSize() {
if (isPreferredSizeSet()) {
return super.getPreferredSize();
}
return new Dimension(PREF_W, PREF_H);
}
}

Change the background color on a custom Button?

I want my button to change color on the mod == 0 of i % 3. The paintComponent(...) is called when the form is re-sized and index is passed in so I would think that this should change the color of my button ever time I start moving the form around the screen.
I have two components on the screen but both will not show up this might be a factor.
Code:
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class testform {
public static void main (String[] p) {
testBall3 j1 = new testBall3();
myButton b1 = new myButton("test");
JPanel testPane = new JPanel();
testPane.setBackground(Color.green);
testPane.setLayout(new BorderLayout());
j1.setPreferredSize(new Dimension(10,10));
//testPane.add(b1);
testPane.add(j1);
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(testPane);
frame.pack();
frame.setSize(300, 200);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
//j1.setColorBall(Color.BLACK);
//j1.repaint();
}
}
class myButton extends JButton {
private static final long serialVersionUID = 1L;
public myButton(String s) {
super(s);
}
public void setPrefferedSize(Dimension d) {
//this.setBounds(x, y, width, height)
setPreferredSize(d);
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
index += i;
System.out.println(i);
if (index % 3 == 0) {
setBackground(Color.RED);
}
else {
setBackground(Color.BLACK);
}
}
}
import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JComponent;
class testBall3 extends JComponent
{
private static final long serialVersionUID = 1L;
private Color colorBall = Color.red;
private int x1, y1;
int index = 0;
public void setColorBall(Color c)
{
this.colorBall = c;
}
public testBall3()
{
super();
System.out.println("MyBall (0)");
}
public testBall3(int x, int y, int diameter)
{
super();
this.setLocation(x, y);
this.setSize(diameter, diameter);
System.out.println("MyBall (1)");
x1 = x;
y1 = y;
}
public void paintBorder(Graphics g)
{
super.paintBorder(g);
g.setColor(Color.YELLOW);
g.fillOval(100, 100, 50, 50);
System.out.println("PaintBorder");
}
public void paintComponent(Graphics g)
{
super.paintComponent(g);
g.setColor(colorBall);
g.fillOval(x1, y1, 10, 10);
System.out.println("paintComponent");
}
public void paint(Graphics g)
{
super.paint(g);
paintComponent(g);
paintBorder(g);
paintChildren(g);
System.out.println("Paint");
}
}

But paintComponent doesn't take a second parameter, how are you passing it? I would think that instead of trying to pass i, you would want make i an attribute of class myButton instead and initialize it to 0 upon instantiation. That is, if you want each button to have its own counter. That sounds like the better plan.

You've got a lot of strange stuff going on...
You've got a component where you override all four major painting methods for no good reason.
In this component, your paint method override calls the super method, and calls the other 3 methods, which in essence will make those 3 methods be called twice.
You've got program logic (advancement of i) inside of your myButton's paintComponent method -- something that should never be done. You do not have full control over when or even if this method is called.
You are calling setBackground(...) from within paintComponent, something which shouldn't be done.
Your class names do not begin with an upper case letter, going against coding conventions, and potentially confusing anyone who tries to read your code.
If you want to change the state of a component on resize, use a ComponentListener.
e.g.
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Toolkit;
import java.awt.Window;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ComponentAdapter;
import java.awt.event.ComponentEvent;
import javax.swing.*;
#SuppressWarnings("serial")
public class Foo2 extends JPanel {
protected static final Color MAGIC_BACKGROUND = Color.red;
protected static final int MAGIC_NUMBER = 3;
private static final int TIMER_DELAY = 20;
private int index = 0;
private JButton myButton = new JButton("My Button");
protected int DELTA_SIZE = 2;
public Foo2() {
add(myButton);
addComponentListener(new ComponentAdapter() {
#Override
public void componentResized(ComponentEvent e) {
index++;
if (index % MAGIC_NUMBER == 0) {
myButton.setBackground(MAGIC_BACKGROUND);
} else {
myButton.setBackground(null);
}
}
});
new Timer(TIMER_DELAY, new ActionListener() {
private Toolkit toolkit = Toolkit.getDefaultToolkit();
private int screenWidth = toolkit.getScreenSize().width;
private int screenHeight = toolkit.getScreenSize().height;
#Override
public void actionPerformed(ActionEvent e) {
if (getWidth() >= screenWidth || getHeight() >= screenHeight) {
((Timer)e.getSource()).stop();
} else {
int width = getWidth() + DELTA_SIZE;
int height = getHeight() + DELTA_SIZE;
setPreferredSize(new Dimension(width, height));
Window win = SwingUtilities.getWindowAncestor(Foo2.this);
win.pack();
win.setLocationRelativeTo(null);
}
}
}).start();
}
private static void createAndShowGui() {
JFrame frame = new JFrame("Foo2");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new Foo2());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}

Scaling image through thread - JAVA

Let say I have an image. I put the image in a JPanel and add the JPanel inside a JFrame. The image moves from the bottom part of the frame to top of the frame while its size is also decreased using AffineTransform. The variable changes using thread.
So here's the following code:
public class SplashScreen extends JFrame{
Image img1;
int w=1,h=1;
int x=0,y=0;
Thread th = new Thread(new Runnable() {
#Override
public void run() {
while(true){
w-=0.05;
h-=0.05;
y-=2;
x+=1;
if(y==-100){
new MainMenu_BlueJay().setVisible(true);
dispose();
}
repaint();
try {
Thread.sleep(10);
} catch (InterruptedException ex) {
Logger.getLogger(SplashScreen.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
});
JPanel p = new JPanel();
public SplashScreen(){
setLayout(new BorderLayout());
p.setPreferredSize(new Dimension(900,600));
p.setBackground(Color.black);
p.setLayout(new GridLayout());
add(p);
setTitle("BlueJay");
setSize(900,600);
getContentPane().setBackground(Color.black);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setLocationRelativeTo(null);
setVisible(true);
th.start();
requestFocus();
setFocusable(true);
}
#Override
public void paint(Graphics g) {
super.paint(g);
Graphics2D g2d = (Graphics2D) g;
img1 = new ImageIcon("images/Intro/BJ Production 2013.png").getImage();
AffineTransform at = new AffineTransform();
at.scale(w,h);
g2d.setTransform(at);
g2d.drawImage(img1, x, y, p);
}
public static void main(String[] args) {
new SplashScreen();
}
However what I get from code above is only black screen. What's the matter? Anyway, If I don't use the AffineTransform function (just move it from bottom to top), the image is shown and moves BUT the frame is flickered (blinking) rapidly.
Any idea to solve this problem so I could move the image while decrease its size and also solve the flickered/rapid blinking frame?

You should not override the paint method of the JFrame. If you want to paint anything, you should paint this in a class that extends JPanel, where you override the paintComponent method.
You should NOT load the image in the painting method. This is horribly inefficient. You should load the image only ONCE, probably in a constructor.
You should not call Graphics2D#setTransform(). Have a look at the JavaDoc at http://docs.oracle.com/javase/7/docs/api/java/awt/Graphics2D.html#setTransform%28java.awt.geom.AffineTransform%29 , which explicitly states
WARNING: This method should never be used to apply a new coordinate transform on top of an existing transform
You should think about your w and h values. Should they be the size of the image that is painted, or used as scaling factors for the image? Setting them as the scaling factors of an AffineTransform will NOT have the effect of scaling an image to the desired size. At the moment, they are declared as int values, so something like w-=0.05 does not really make sense anyhow.
You should have a clear idea of how you are going to describe the animation that the image should perform.
One could possibly summarize this:
You should not write code and assume it is "correct" only because there are no compilation errors ;-)
However, the following snippet may be a first step towards your goal:
package stackoverflow;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class SplashScreen extends JFrame
{
public static void main(String[] args)
{
SwingUtilities.invokeLater(new Runnable()
{
#Override
public void run()
{
new SplashScreen();
}
});
}
private PaintPanel paintPanel;
public SplashScreen()
{
setTitle("BlueJay");
setDefaultCloseOperation(EXIT_ON_CLOSE);
getContentPane().setBackground(Color.BLACK);
getContentPane().setLayout(new BorderLayout());
paintPanel = new PaintPanel();
getContentPane().add(paintPanel, BorderLayout.CENTER);
setSize(900,600);
setLocationRelativeTo(null);
setFocusable(true);
requestFocus();
setVisible(true);
startAnimation();
}
void startAnimation()
{
Thread thread = new Thread(new Runnable()
{
int x = 100;
int y = 100;
int w = 0;
int h = 0;
#Override
public void run()
{
try
{
Thread.sleep(500);
}
catch (InterruptedException ex)
{
Thread.currentThread().interrupt();
return;
}
while (true)
{
if (y == 200)
{
// new MainMenu_BlueJay().setVisible(true);
dispose();
}
x += 2;
y += 1;
w += 1;
h += 1;
paintPanel.setImageCoordinates(x, y, w, h);
repaint();
try
{
Thread.sleep(10);
}
catch (InterruptedException ex)
{
Thread.currentThread().interrupt();
return;
}
}
}
});
thread.start();
}
}
class PaintPanel extends JPanel
{
private final Image image;
private int imageX, imageY;
private int imageW, imageH;
PaintPanel()
{
image = new ImageIcon("Clipboard02.jpg").getImage();
imageX = 0;
imageY = 0;
imageW = 0;
imageH = 0;
}
void setImageCoordinates(int imageX, int imageY, int imageW, int imageH)
{
this.imageX = imageX;
this.imageY = imageY;
this.imageW = imageW;
this.imageH = imageH;
repaint();
}
#Override
protected void paintComponent(Graphics gr)
{
super.paintComponent(gr);
Graphics2D g = (Graphics2D) gr;
float scalingX = (float) imageW / image.getWidth(null);
float scalingY = (float) imageH / image.getHeight(null);
g.scale(scalingX, scalingY);
int ix = (int)(imageX / scalingX);
int iy = (int)(imageY / scalingY);
g.drawImage(image, ix, iy, null);
}
}

Don't paint on top-level containers like JFrame. Instead use a JPanel and override its paintComponent method and call super.paintComponent
No need to call Thread.sleep(). Instead Use a javax.swing.Timer.
Run your program from the EDT
Don't create a new ImageIcon in the paint method. It will create new ImageIcon object every time repaint() is called. Instead, instantiate it in the constructor.
Here's a refactor of the code.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class SplashScreen extends JFrame {
Image img1;
int w = 900, h = 600;
int x = 0, y = 0;
public SplashScreen() {
setLayout(new BorderLayout());
add(new MyPanel());
setTitle("BlueJay");
setSize(900, 600);
getContentPane().setBackground(Color.black);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setLocationRelativeTo(null);
setVisible(true);
requestFocus();
setFocusable(true);
}
private class MyPanel extends JPanel {
public MyPanel() {
img1 = new ImageIcon(SplashScreen.class.getResource("/resources/stackoverflow5.png")).getImage();
setBackground(Color.black);
setLayout(new GridLayout());
Timer timer = new Timer(20, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
w -= 5;
h -= 5;
y -= 2;
x += 1;
if (y == -250) {
new MainMenu_BlueJay().setVisible(true);
dispose();
}
repaint();
}
});
timer.start();
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
//AffineTransform at = new AffineTransform();
// at.scale(w, h);
// g2d.setTransform(at);
g2d.drawImage(img1, x, y, w, h, this);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(900, 600);
}
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new SplashScreen();
}
});
}
}
I'm not too familiar with Graphics2D so I commented out the AffirmTransformation stuff, but fixed your other problems.

I am trying to display a JPEG image in java

I have an assignment that I am doing where I am supposed to implement and design an application that plays a game called catch the creature. Have the creature appear at a random location then disappear and reappear somewhere else. The goal is to "catch" the creature by clicking the creature with a mouse button. Record the number of times the creature is caught.
I need help just displaying the creature which is an JPEG of a pikachu, I have tried a few things but none of them work. Any help is appreciated thank you!
Main Code:
import javax.swing.*;
public class Catch_The_Creature
{
public static void main(String[] args)
{
JFrame frame = new JFrame("Catch the Creature");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Creature panel = new Creature();
JOptionPane.showMessageDialog(frame, "Catch Pikachu!");
frame.getContentPane().add(panel);
frame.pack();
frame.setVisible(true);
}
}
Creature Code:
import java.awt.*;
import java.util.Random;
import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
public class Creature extends JPanel
{
private final int WIDTH = 400, HEIGHT = 300;
private final int DELAY=20, IMAGE_SIZE = 60;
private ImageIcon image;
private int pikachuX, pikachuY;
private int x, y;
private int catchCount=0;
private static Random generator = new Random();
private Timer time;
private ActionListener updater;
private JLabel countLabel;
public Creature()
{
image = new ImageIcon("image/pikachu.jpg");
time = new Timer(DELAY, updater);
addMouseListener ((MouseListener) new MouseClickedListener());
setBackground (Color.green);
setPreferredSize(new Dimension(1900,1000));
time.start();
}
public boolean point(int x, int y)
{
if (x == pikachuX && y == pikachuY)
{
catchCount++;
return true;
}
return false;
}
public int getCatchCount()
{
return catchCount;
}
private class MouseClickedListener extends MouseAdapter
{
public void mouseClicked(MouseEvent event)
{
point(event.getX(), event.getY());
}
}
public void paintComponent(Graphics page)
{
super.paintComponent(page);
page.drawImage(image.getImage(),WIDTH, HEIGHT, null);
page.drawString("Pikachus Captured: " + catchCount, 10, 35);
setFont(new Font("Arial", Font.BOLD,35));
}
public void actionPerformed(ActionEvent event)
{
time.setDelay(1000);
x += pikachuX;
y += pikachuY;
if (x <= 0 || x >= WIDTH-IMAGE_SIZE)
pikachuX = pikachuX * -1;
if (y <= 0 || y >= HEIGHT-IMAGE_SIZE)
pikachuY = pikachuY * -1;
repaint();
}
public void mouseEntered(MouseEvent arg0) {}
public void mouseExited(MouseEvent arg0) {}
public void mousePressed(MouseEvent arg0) {}
public void mouseReleased(MouseEvent arg0){}
}

It doesn't look like you ever add the ImageIcon to the panel or tell it to paint in the paintComponent() method.
First solution [Preferred]: Add ImageIcon to the panel. In the constructor
super.add(image);
Make sure you use the correct layout (probably a null or absolute layout) and that you update the coordinates of the ImageIcon itself, not just some member variables.
Second solution: Paint the ImageIcon in the paintComponent() method. This is probably discouraged because it goes against the general Swing principles.

Make sure your Image file is in the right directory. If you're running from netbeans or eclipse your file structure should look like this
ProjectRoot
src
bin
image
pikachu.jpeg
Since you are using "image/pikachu.png", you image filder should be a child of the project root folder as that's where the IDE will first search fore your file path
Edit: To draw image. Instead of using ImageIcon, use BufferedImage
try {
BufferedImage image = ImageIO.read("image/pikachu.jpeg");
} catch (Exception ex){
ex.printStackTrace();
}
public void paintComponent(Graphics page)
{
super.paintComponent(page);
page.drawImage(image, x, y, heightYouWant, widthYouWant, this);
page.drawString("Pikachus Captured: " + catchCount, 10, 35);
setFont(new Font("Arial", Font.BOLD,35));
}

All i needed to do was put values on where I wanted the picture to start at in the constructor.
public Creature()
{
image = new ImageIcon ("pikachu.png");
time = new Timer(DELAY, updater);
x = 0;
y = 50;
addMouseListener ((MouseListener) new MouseClickedListener());
setBackground (Color.green);
setPreferredSize(new Dimension(1900,1000));
time.start();
}
While still using an Image Icon and still paint the image in the paint component.
public void paintComponent(Graphics page)
{
super.paintComponent(page);
image.paintIcon (this, page, x, y);
page.drawString("Pikachus Captured: " + catchCount, 10, 35);
setFont(new Font("Arial", Font.BOLD,35));
}

paintComponent does not work if its called by the recursive function?

I want to see all the Points one after another but I see only able to see 1
point. What shold I change to see all the Points ?
In the System.out you can see 10 times "set" and then 2 times
"paintComponent". what should I change that after each time set is
called it change the "paintComponente" ?
==================================================================================
public class exampe extends JPanel
{
int x;
int y;
public void paintComponent(Graphics g)
{
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.fillOval(x-2,y-2,4,4);
System.out.println("paintComponent");
}
public void set(int X, int Y)
{
x = X;
y = Y;
System.out.println("set");
super.repaint();
}
public static void main(String args[])
{
int e=1;
JFrame frame = new JFrame("TEST");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
exampe ex= new exampe();
JScrollPane scroll = new JScrollPane(ex);
frame.getContentPane().add(scroll);
frame.setSize(400, 300);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
for(int i=0; i< 10; ++i)
ex.set(e+i,e+i);
}
}

*SIMPLE EXPLANATION AS TO WHY YOU COULD ONLY SEE THE LAST UPDATE : *
A quote taken from Filthy Rich Clients by Chet Haase and Romain Guy
It is important to note that repaint requests get “coalesced,” or combined.
So, for example, if you request a repaint and there is already one on the
queue that has not yet been serviced, then the second request is ignored
because your request for a repaint will already be fulfilled by the earlier
request. This behavior is particularly helpful in situations where many
repaint requests are being generated, perhaps by very different situations
and components, and Swing should avoid processing redundant requests and
wasting effort.
Try your hands on this, and ask what is not clear to you :
import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import javax.swing.*;
public class PointsExample
{
private CustomPanel contentPane;
private Timer timer;
private int x = 1;
private int y = 1;
private ActionListener timerAction = new ActionListener()
{
public void actionPerformed(ActionEvent ae)
{
contentPane.set(x, y);
x++;
y++;
if (x == 450)
timer.stop();
}
};
/*
* This is just JFrame, that we be
* using as the Base for our Application.
* Though here we are calling our
* JPanel (CustomPanel), whose
* paintComponent(...) method, we had
* override.
*/
private void createAndDisplayGUI()
{
JFrame frame = new JFrame("Locate Mouse Position");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
contentPane = new CustomPanel();
frame.setContentPane(contentPane);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
timer = new Timer(100, timerAction);
timer.start();
}
public static void main(String\u005B\u005D args)
{
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
new PointsExample().createAndDisplayGUI();
}
});
}
}
class CustomPanel extends JComponent
{
private int x;
private int y;
public void set(int a, int b)
{
x = a;
y = b;
repaint();
}
#Override
public Dimension getPreferredSize()
{
return (new Dimension(500, 500));
}
#Override
public void paintComponent(Graphics g)
{
g.clearRect(0, 0, getWidth(), getHeight());
Graphics2D g2 =(Graphics2D) g;
g2.fillOval(x, y, 4, 4);
}
}
Here is the code, that will allow you to have a look at your points while iterating inside a for loop, though this approach is highly discouraged, for many cons associated with it. Though try your hands on this instead of calling repaint() call paintImmediately(int ...) or paintImmediately(Rectangle rect)
import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import javax.swing.*;
public class PointsExample
{
private CustomPanel contentPane;
private Timer timer;
private int x = 1;
private int y = 1;
/*
* This is just JFrame, that we be
* using as the Base for our Application.
* Though here we are calling our
* JPanel (CustomPanel), whose
* paintComponent(...) method, we had
* override.
*/
private void createAndDisplayGUI()
{
JFrame frame = new JFrame("Locate Mouse Position");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
contentPane = new CustomPanel();
frame.setContentPane(contentPane);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
for (int i = 0; i < 500; i++)
{
contentPane.set(x, y);
x++;
y++;
if (x == 450)
break;
}
}
public static void main(String\u005B\u005D args)
{
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
new PointsExample().createAndDisplayGUI();
}
});
}
}
class CustomPanel extends JComponent
{
private int x;
private int y;
public void set(int a, int b)
{
x = a;
y = b;
paintImmediately(0, 0, getWidth(), getHeight());
}
#Override
public Dimension getPreferredSize()
{
return (new Dimension(500, 500));
}
#Override
public void paintComponent(Graphics g)
{
super.paintComponent(g);
g.fillOval(x, y, 4, 4);
}
}

1: first line of paintComponent() should be your super.paintComponent()
2: why are you calling super.repaint(), make it simply repaint()
Your Drow should be like this.
public class drow extends JPanel {
...........
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 =(Graphics2D) g;
}
public void set_list(LinkedList <point> p){
Points =p;
repaint();
}
try with this.
i hope this is simply a structure, your paintComponent() isn't drawing anything.
EDIT
public void set_list(LinkedList <point> p){
Points =p;
System.out.println("set_ist");// 1:First this line will be displayed then..
repaint();//2: Then this is called, which in turn calls your `paintComponent()`
}
Now when your paintComponent() is called it has
system.out.println("paintComponent");
//3: so now this will be displayed.
Where is the problem here?
EDIT- SWING TIMER
Your code was ok, but the function processing is way faster than GUI updation, thats why you were unable to see the changes in front of you. The way you were doing, of calling thread.sleep() between function calls to slow down it's call, was not a good approach. For any timing thing's in swing, use swing timer, i changed your code for swing timer.
Using Swing Timer:
public class exampe extends JPanel implements ActionListener {
int x;
int y;
int temp = 0;
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.fillOval(x - 2, y - 2, 4, 4);
}
public void set(int X, int Y) {
x = X;
y = Y;
}
public static void main(String args[]) {
JFrame frame = new JFrame("TEST");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
exampe ex = new exampe();
JScrollPane scroll = new JScrollPane(ex);
frame.getContentPane().add(scroll);
frame.setSize(400, 300);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
Timer PointTimer = new Timer(1000, ex);
PointTimer.setInitialDelay(1000);
PointTimer.start();
System.out.println("started");
}
#Override
public void actionPerformed(ActionEvent e) {
// set(rand.nextInt(350), rand.nextInt(350));
set(temp+10,temp+10);
temp=temp+2;
repaint();
}
}