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Java -Repaint() not working when i want to call it

I wonder why the repiant() method is not working as intended. My Code:
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JPanel;
public class RightPanel extends JPanel implements ActionListener{
JButton buttono;
JButton buttonu;
MyFrame frame;
ButtomPanel s;
public RightPanel(MyFrame frame){
super();
this.frame=frame;
s= new ButtomPanel(frame);
this.setPreferredSize(new Dimension((frame.getWidth()/3),frame.getHeight()));
setBackground(Color.green);
setLayout(new BorderLayout());
buttono = new JButton ("up");
buttonu = new JButton ("down");
buttono .addActionListener(this);
buttonu .addActionListener(this);
add(buttono , BorderLayout.NORTH);
add(buttonu , BorderLayout.SOUTH);
setVisible(true);
}
#Override
public void actionPerformed(ActionEvent e) {
if (e.getSource()==buttono) {
System.out.println("Up");
s.x=s.x+10;
s.repaint();
}
}
I want to Repaint following class:
import java.awt.Color;
import java.util.Timer;
import java.util.TimerTask;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.image.BufferedImage;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JLabel;
import javax.swing.JPanel;
public class ButtomPanel extends JPanel {
MyFrame frame;
BufferedImage image;
boolean geklickt=false;
public static int x=0;;
public ButtomPanel(MyFrame frame) {
super();
this.frame=frame;
this.setPreferredSize(new Dimension(((frame.getWidth()/3)*2),585));
setBackground(Color.blue);
java.net.URL resource = getClass().getResource("/resources/siegel.jpg");
try {
image = ImageIO.read(resource);
} catch (IOException e) {
e.printStackTrace();
}
setVisible(true);
}
public void paint(Graphics g) {
super.paint(g);
g.drawImage(image, 150+x, 150+x, 150, 150, null);}
}
}
I want to change with the ActionListener in the RightPanel Class the x from the BottomPanel Class and then repaint it, but it doesnt work. I can raise the x, but s.repaint() does not call the paint-Method.

s is never added to anything, so it will never be painted.
this.setPreferredSize(new Dimension((frame.getWidth()/3),frame.getHeight())); is a horribly bad idea. The window should be conforming to the size of the components, not the other way round. In fact, there's never really a good reason to expose MyFrame to the components this way, it provides these components control over MyFrame which they should never have.
java.net.URL resource = getClass().getResource("/resources/siegel.jpg");
try {
image = ImageIO.read(resource);
} catch (IOException e) {
e.printStackTrace();
}
is a bad idea. The class should be throwing the exception to those using it, so that they know something has gone wrong. Doing it this way not only consumes the error in a way which is difficult to trace, but also sets you up for a NullPointerException when you call g.drawImage(image, 150+x, 150+x, 150, 150, null)
Don't override paint
public void paint(Graphics g) {
super.paint(g);
g.drawImage(image, 150+x, 150+x, 150, 150, null);
}
prefer paintComponent instead. paint is actually a very complex method. See Painting in AWT and Swing and Performing Custom Painting for more details
public static int x=0; is a bad idea for a three reasons:
static is not your friend. What happens when you have more than one instance of ButtomPanel? Generally speaking, when you use static in this way, it's a red flag telling you that your design is wrong.
public is providing uncontrolled access to the property. This is generally discouraged and you could be preferring to use setters and getters to interact with the property.
JPanel already has a x property, which could make it confusing (ie if if someone used getX instead of x). Better to rename it to something like imageX of imageXOffset.
Runnable example...
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public final class Main {
public static void main(String[] args) {
new Main();
}
public Main() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
JFrame frame = new JFrame();
frame.add(new RightPanel());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
} catch (IOException ex) {
Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
}
}
});
}
public class RightPanel extends JPanel implements ActionListener {
JButton buttono;
JButton buttonu;
ButtomPanel s;
public RightPanel() throws IOException {
super();
s = new ButtomPanel();
setBackground(Color.green);
setLayout(new BorderLayout());
buttono = new JButton("up");
buttonu = new JButton("down");
buttono.addActionListener(this);
buttonu.addActionListener(this);
add(buttono, BorderLayout.NORTH);
add(buttonu, BorderLayout.SOUTH);
add(s);
setVisible(true);
}
#Override
public void actionPerformed(ActionEvent e) {
if (e.getSource() == buttono) {
System.out.println("Up");
s.addToImageXOffset(10);
}
}
}
public class ButtomPanel extends JPanel {
private BufferedImage image;
private int imageXOffset = 0;
public ButtomPanel() throws IOException {
super();
setBackground(Color.blue);
image = ImageIO.read(getClass().getResource("/images/Heart.png"));
}
#Override
public Dimension getPreferredSize() {
return new Dimension(400, 400);
}
public void addToImageXOffset(int delta) {
setImageXOffset(getImageXOffset() + delta);
}
public void setImageXOffset(int imageXOffset) {
this.imageXOffset = imageXOffset;
repaint();
}
public int getImageXOffset() {
return imageXOffset;
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g); //To change body of generated methods, choose Tools | Templates.
g.drawImage(image, 150 + imageXOffset, 150 + imageXOffset, this);
}
}
}

Repaint() does not work after adding more components to JPanel in Swing, Java

I am starting with Java and want to make a simple pong game to get into the ways of displaying stuff in java. I have created 2 classes that both extend JPanel and call the repaint() function every 16.6 milliseconds. I added both to a JPanel which I added to the frame, but only the component I added first displays.
I've tried to revalidate() after repaint() in both classes and made sure that the Timer actually works and that it's actionPerformed() method is actually called.
This is the main method:
public class Main {
public static void main(String[] args){
JFrame frame = new JFrame("Pong");
//...
JPanel mainPanel = new JPanel();
mainPanel.add(new Player());
mainPanel.add(new Ball(frameWidth/2, frameHeight/2 -40));
frame.add(mainPanel);
}
}
This is the important code for the classes (It's basically the same for both of them):
public class Player extends JPanel {
public Player(){
setPreferredSize(new Dimension(Main.frameWidth, Main.frameHeight));
setBackground(Color.BLACK);
new Timer(1000/60, new ActionListener(){
public void actionPerformed(ActionEvent e){
update();
repaint();
}
}).start();
}
//...
public void paintComponent(Graphics g){
super.paintComponent(g);
g.setColor(Color.WHITE);
g.fillRect(x, y, width, height);
}
}
(Of coure I left things like #Override or unneseccary functions out to shorten the code)
This code only paints the Player, altough I want it to display all the components of mainPanel.
This is an example that you can (hopefully) run. I had to split it up into 3 files, since I suck at anonymus classes:
Main.java
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Main {
public static void main(String[] args){
JFrame frame = new JFrame("Pong");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(800, 800);
JPanel mainPanel = new JPanel();
mainPanel.add(new Player());
mainPanel.add(new Ball());
frame.add(mainPanel);
frame.setVisible(true);
}
}
///////
Player.java
//////
import javax.swing.JPanel;
import javax.swing.Timer;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Color;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class Player extends JPanel{
private int x = 20, y = 300, width = 20, height = 100;
public Player(){
setPreferredSize(new Dimension(800, 800));
setBackground(Color.BLACK);
new Timer(1000/60, new ActionListener(){
#Override
public void actionPerformed(ActionEvent e){
repaint();
}
}).start();
}
#Override
public void paintComponent(Graphics g){
super.paintComponent(g);
g.setColor(Color.WHITE);
g.fillRect(x, y, width, height);
}
}
//////
Ball.java
//////
import javax.swing.JPanel;
import javax.swing.Timer;
import java.awt.Graphics;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class Ball extends JPanel{
private int x = 20, y = 300, width = 20, height = 100;
public Ball(){
setPreferredSize(new Dimension(800, 800));
setBackground(Color.BLACK);
new Timer(1000/60, new ActionListener(){
#Override
public void actionPerformed(ActionEvent e){
repaint();
}
}).start();
}
#Override
public void paintComponent(Graphics g){
super.paintComponent(g);
g.setColor(Color.WHITE);
g.fillRect(x, y, width, height);
}
}

In method paintComponent() of class Player, you paint the exact same Rectangle each time. In order to achieve animation, each time you paint the rectangle you need to change either its size or location or both. What do you expect the Player to do? Should it move up and down along the left edge of the window? Have you seen the lesson entitled How to Use Swing Timers which is part of Oracle's Java Tutorial?
EDIT
I see now that Player hides Ball, because of the default layout manager of JPanel. The below code is essentially the code you posted but I set GridLayout as the layout manager for mainPanel. Also, a java source code file may contain more than one class but exactly one class must be public. Hence in the below code only class Main is public.
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
public class Main {
public static void main(String[] args) {
JFrame frame = new JFrame("Pong");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel mainPanel = new JPanel(new GridLayout(0, 2));
mainPanel.add(new Player());
mainPanel.add(new Ball());
frame.add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
}
class Player extends JPanel {
public Player() {
setBorder(BorderFactory.createLineBorder(Color.RED, 2, false));
setPreferredSize(new Dimension(800, 800));
setBackground(Color.BLACK);
new Timer(1000 / 60, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
repaint();
}
}).start();
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.WHITE);
g.fillRect(20, 100, 20, 100);
}
}
class Ball extends JPanel {
public Ball() {
setBorder(BorderFactory.createLineBorder(Color.CYAN, 2, false));
setPreferredSize(new Dimension(800, 800));
setBackground(Color.BLACK);
new Timer(1000 / 60, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
repaint();
}
}).start();
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.WHITE);
g.fillRect(300, 300, 10, 10);
}
}
And here is a screen capture of the GUI...

I just realized that if I extend my window manually, the second JPanel shows up under the one responsible for the Player! This means that I'll need to set the Panels position somehow, right?
#Abra

GUI Application that allows the user to choose the shape and color of a drawing

I need to create a program that allows the user to select a color from a list of checkboxes, red and blue, and then a shape from a
list of radio buttons, square or circle. When the “Draw” button is pressed the selected
shape and color are drawn. If both red and blue are chosen, the shape is drawn in purple.
should look like the following picture:
This is about as far i've gotten, stumped as to how to create the circle and print it when that option is chosen. Also how do I reorganize the labels and buttons?
any help is appreciated
import java.awt.GridBagLayout;
import java.io.PrintWriter;
import java.util.Scanner;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Shapes
{
public static JFrame window = new JFrame("Shapes");
public static JPanel panel = new JPanel(new GridBagLayout());
public static void main(String[] args)
{
window.setBounds(0, 0,300, 300);
window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
window.add(panel);
MApp m = new MApp();
m.setBounds(100,100,100,100);
window.add(m);
Draw d = new Draw(panel) ;
d.setBounds(0, 0, window.getWidth(), 90);
window.add(d);
window.setVisible(true);
}
}
import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.JPanel;
public class MApp extends JPanel implements MouseListener
{
private boolean clicked;
private Rectangle r;
public MApp()
{
clicked = false;
r = new Rectangle(15, 15, 50, 50);
addMouseListener(this);
}
public void paintComponent(Graphics g)
{
if(clicked)
{
g.setColor(Color.BLUE);
}
else
{
g.setColor(Color.RED);
}
g.fillRect((int)r.getX(), (int)r.getY(),
(int)r.getWidth(), (int)r.getHeight());
}
public void mouseClicked (MouseEvent e)
{
Point p = new Point(e.getX(),e.getY());
if(r.contains(p))
{
clicked = !clicked;
}
repaint();
}
public void Circle()
{
g.fillOval(0, 0, s, s);
}
public void mousePressed (MouseEvent evnt) {}
public void mouseReleased (MouseEvent evnt) {}
public void mouseEntered (MouseEvent evnt) {}
public void mouseExited (MouseEvent evnt) {}
}
import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Panel;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.ButtonGroup;
import javax.swing.GroupLayout;
import javax.swing.JButton;
import javax.swing.JCheckBox;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.JTextField;
public class Draw extends JPanel implements ActionListener
{
JTextField tfInfo;
JLabel lblColor, lblShapes;
JCheckBox cbRed, cbBlue;
ButtonGroup shapes;
JRadioButton rbCircle, rbSquare;
JButton btnSubmit;
public Draw(JPanel panel)
{
GridBagConstraints c = new GridBagConstraints();
tfInfo = new JTextField("Color", 15);
tfInfo = new JTextField("Shapes", 50);
lblColor = new JLabel("Colors:");
cbRed = new JCheckBox("Red");
cbBlue = new JCheckBox("Blue");
lblShapes = new JLabel("Shapes:");
shapes = new ButtonGroup();
rbCircle = new JRadioButton("Circle");
rbSquare = new JRadioButton("Square");
btnSubmit = new JButton("Draw");
btnSubmit.addActionListener(this);
this.setBackground(Color.WHITE);
add(lblColor);
add(cbRed);
add(cbBlue);
add(lblShapes);
add(rbCircle);
add(rbSquare);
add(btnSubmit);
shapes.add(rbCircle);
shapes.add(rbSquare);
}
public void actionPerformed(ActionEvent a)
{
if(a.getSource() == btnSubmit)
{
if(cbRed.isSelected()&&cbBlue.isSelected())
{
if(rbCircle.isSelected())
{
}
else if(rbSquare.isSelected())
{
}
}
else if(cbRed.isSelected())
{
if(rbCircle.isSelected())
{
}
else if(rbSquare.isSelected())
{
}
}
else if(cbBlue.isSelected())
{
if(rbCircle.isSelected())
{
}
}
else if(rbSquare.isSelected())
{
}
}
repaint();
}
}

Start by separating your "management" code from you "painting" code
You should have a single class that only handles the painting of the shape, nothing else, it just does what it's told.
You should then have a second class which takes input from the user and when they press the Draw button, it tells the "paint" class what it should be paint, for example...
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.ButtonGroup;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class DrawStuff extends JFrame {
public static void main(String[] args) {
new DrawStuff();
}
public DrawStuff() {
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 ControlPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class ControlPane extends JPanel {
private JRadioButton circle;
private JRadioButton square;
private DrawPane drawPane;
public ControlPane() {
setLayout(new GridBagLayout());
ButtonGroup bg = new ButtonGroup();
circle = new JRadioButton("Circle");
square = new JRadioButton("Square");
bg.add(circle);
bg.add(square);
GridBagConstraints gbc = new GridBagConstraints();
gbc.gridwidth = GridBagConstraints.REMAINDER;
gbc.weightx = 1;
JPanel shape = new JPanel();
shape.add(circle);
shape.add(square);
add(shape, gbc);
JButton draw = new JButton("Draw");
draw.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
if (circle.isSelected()) {
drawPane.setDrawableShape(DrawableShape.CIRCLE);
} else if (square.isSelected()) {
drawPane.setDrawableShape(DrawableShape.SQUARE);
}
}
});
gbc.gridwidth = GridBagConstraints.REMAINDER;
add(draw, gbc);
drawPane = new DrawPane();
gbc.weightx = 1;
gbc.weighty = 1;
gbc.fill = gbc.BOTH;
add(drawPane, gbc);
}
}
public enum DrawableShape {
CIRCLE,
SQUARE
}
public class DrawPane extends JPanel {
private DrawableShape drawableShape;
public DrawPane() {
}
public void setDrawableShape(DrawableShape drawableShape) {
this.drawableShape = drawableShape;
repaint();
}
public DrawableShape getDrawableShape() {
return drawableShape;
}
#Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
DrawableShape shape = getDrawableShape();
if (shape != null) {
int width = getWidth() - 20;
int height = getHeight() - 20;
int size = Math.min(width, height);
int x = (getWidth() - size) / 2;
int y = (getHeight() - size) / 2;
if (shape == DrawableShape.CIRCLE) {
g2d.fillOval(x, y, size, size);
} else if (shape == DrawableShape.SQUARE) {
g2d.fillRect(x, y, size, size);
}
}
g2d.dispose();
}
}
}
I'll leave you to add in the color management.
Have a closer look at:
How to Use Buttons, Check Boxes, and Radio Buttons
How to Write an Action Listeners
Painting in AWT and Swing
Performing Custom Painting
2D Graphics
for more details

Java is drawing 2 boxes

So I am making a little game to learn some graphical java and I am having trouble with a button. It is drawing 2, one is the correct size and in the correct location and then there is a very small button centered at the top of the application. THere should only be the one button at (0,0,200,50). I do not know what is wrong but here is the code for the button, if you need something more then this let me know!
ImageIcon test = new ImageIcon("nhButton.png");
JButton jb = new JButton(test);
jb.setBounds(0, 0, 200, 50);
jb.setVisible(true);
add(jb);
EDIT1: the 2 classes where error will be: board.java:
import javax.swing.JPanel;
import javax.swing.JButton;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class Board extends JPanel {
public Board() {
}
#Override
public void paintComponent(Graphics g) {
ImageIcon test = new ImageIcon("nhButton.png");
JButton jb = new JButton(test);
jb.setBounds(0, 0, 200, 50);
jb.setVisible(true);
add(jb);
}
private void drawRectangle(Graphics g, int x, int y, int width, int height) {
Graphics2D g2d = (Graphics2D) g;
g2d.drawRect(x, y, width, height);
}
}
and the main:
import java.awt.EventQueue;
import java.awt.GraphicsEnvironment;
import java.awt.Toolkit;
import javax.swing.JFrame;
public class main extends JFrame {
public main() {
initUI();
}
private void initUI() {
add(new Board());
setSize(800, 600);
setTitle("Application");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setLocationRelativeTo(null);
}
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
main ex = new main();
ex.setVisible(true);
}
});
}
}

If you try to resize window, you will see that buttons are spawning.
This happens because of your paintComponent method, which is called every painting iteration.
You should move button addition, for example, to constructor which is called once:
public Board() {
ImageIcon test = new ImageIcon("nhButton.png");
JButton jb = new JButton(test);
jb.setBounds(0, 0, 200, 50);
jb.setVisible(true);
add(jb);
}

paintComponent draws other components on top of my drawing

I'm trying to build a simple paint tool. The mouseDrag events creates a new ellipse and causes my JPanel to repaint().
This works fine so far.
However, if I press any button (or any other UI component) before firing the mouseDrag event for the first time, the button is painted in the upper left corner of my panel.
I have isolated the code into this test application:
import java.awt.BasicStroke;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Test extends JFrame
{
public Test()
{
final JPanel paintPanel = new JPanel(){
#Override
protected void paintComponent(Graphics g)
{
Graphics2D g2d = (Graphics2D)g;
g2d.setPaintMode();
g2d.setStroke(new BasicStroke(1));
g2d.fillRect(100, 100, 10, 10);
}
};
paintPanel.setPreferredSize(new Dimension(300,300));
paintPanel.addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e)
{
paintPanel.repaint();
}
});
this.setLayout(new FlowLayout());
this.add(paintPanel);
this.add(new JButton("Dummy"));
this.pack();
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setVisible(true);
}
public static void main(String... args)
{
new Test();
}
}
A Screenshot for "seeing" the problem in my Main application

+1 to #MadProgrammer's answers.
You should have super.paintComponent(..) as the first call in your overriden paintComponent()
Do not extend JFrame unnecessarily
Create and minipulate Swing components via EDT
Dont call setPrefferedSize() rather override getPrefferedSize()
Here is an example which incorporates my advice's and #MadProgrammer's:
import java.awt.BasicStroke;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class Test {
JFrame frame;
public Test() {
frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
final PaintPanel paintPanel = new PaintPanel();
paintPanel.addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
paintPanel.addRect(e.getX(), e.getY());
}
});
frame.setLayout(new FlowLayout());
frame.add(paintPanel);
frame.add(new JButton("Dummy"));
frame.pack();
frame.setVisible(true);
}
public static void main(String... args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new Test();
}
});
}
}
class PaintPanel extends JPanel {
public PaintPanel() {
addRect(100, 100);
}
ArrayList<Rectangle> rects = new ArrayList<>();
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
g2d.setPaintMode();
for (Rectangle r : rects) {
g2d.setStroke(new BasicStroke(1));
g2d.fillRect(r.x, r.y, r.width, r.height);
}
}
public void addRect(int x, int y) {
rects.add(new Rectangle(x, y, 10, 10));
repaint();
}
#Override
public Dimension getPreferredSize() {
return new Dimension(300, 300);
}
}

You're not calling super.paintComponent.
The graphics context used for a paint cycle is shared between all the components begin painted, this means if you don't take care to clear it before painting onto, you will end up with what ever was painted before you.
One of the jobs of paintComponent is to prepare the graphics for painting