Develop Reference

How to move around an object drawn on a panel with button click

I am trying to build a bounce game in Java. My project has three classes ie the Main class which creates a new window(frame) where the game buttons and bounce objects are drawn.
The GameInterface class which represents the properties of the frame being drawn and the RightPanel class which I created so that I could override the paint(Graphics) method to draw my bounce object. So far this is what I have managed to draw with the code.
You can see that I have two JPanels, one that holds my buttons and the other one that accepts the drawing of a round ball on it ie RightPanel
I need help with the Button Event listeners to move the ball up and down and when user holds the button down, it needs to keep moving down until reaches the down order, sam for the up button.
The code am using is provided below.
GameInterface class
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
public class GameInterface extends JFrame {
//we need this panel declaration in the class level for reference from other methods
RightPanel rightpanel;
//define the physical properties of the window
public GameInterface(){
setSize(new Dimension(600, 600));
setResizable(false);
setTitle("Bounce Game");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBackground(Color.black);
//define a new JSplitPane and use it to add two JPanels
JPanel leftpanel= new JPanel();
//add buttons to the left panel programatically
JButton up= new JButton("Move up");
//set the event listeners for the buttons
up.addActionListener(new AbstractAction() {
#Override
public void actionPerformed(ActionEvent e) {
//move my ball up
//clear and redraw the ball while in a new position, use a timer or
something
}
});
JButton down = new JButton("Move down");
down.addActionListener(new AbstractAction() {
#Override
public void actionPerformed(ActionEvent e) {
//move my ball down
// rightpanel.getGraphics.fillColor(Color.RED);
}
});
leftpanel.add(up);
leftpanel.add(down);
//add a new RightPanel with a drawn red object
rightpanel= new RightPanel();
JSplitPane splitpane= new JSplitPane(JSplitPane.HORIZONTAL_SPLIT,leftpanel,rightpanel);
this.add(splitpane);
setVisible(true);
}
}
RightPanel class
import javax.swing.*;
import java.awt.*;
public class RightPanel extends JPanel {
//define the position where the circle will be drawn
private int positionX=150;
private int positionY=150;
//I had an idea where we need a timer and then on delay we
//decrement positionX by 3 for move down but can't figure out how to clear RightPanel
private int radius=100;//as the shape is a circle
//override the paint method to draw the bounce ball on the second panel
#Override
public void paint(Graphics g) {
g.setColor(Color.RED);
g.fillOval(positionX,positionY,radius,radius);
}
}
Main class
public class Main
{
public static void main(String args[]){
new GameInterface();
}
}
How do I add logic to my code to make it move the circle up an down, Thank You.
I tried using a timer object to clear the panel and then redraw the ball in the new position of the ball but it draws a vertical bar, not clearing the original ball drawn.

Never call getGraphics() on a component.
Override paintComponent not paint
Call the super.paintComponent(g) in your override.
Give the RightPanel class setter methods that allow you to change the positionX and positionY locations for drawing,
In the button listener, call an appropriate setter method, and then call repaint() on on the RightPanel instance after changing the positions.
For example:
The key code below is here in the ActionListener where you update the position values and call repaint:
moveRightBtn.addActionListener(e -> {
// get and update the x position
int x = drawOval.getPositionX();
x += DELTA;
// call the setter method
drawOval.setPositionX(x);
// request that Java repaint the JPanel
drawOval.repaint();
});
and in the drawing JPanel's paintComponent method where you call the super's method and draw the oval:
#Override
protected void paintComponent(Graphics g) {
// this is needed to do house-keeping painting, to clear "dirty" pixels
super.paintComponent(g);
// this is needed to draw smooth graphics
Graphics2D g2 = (Graphics2D) g;
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
g2.setColor(OVAL_COLOR);
g2.fillOval(positionX, positionY, RADIUS, RADIUS);
}
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import javax.swing.*;
#SuppressWarnings("serial")
public class MoveCircle extends JPanel {
private static final int DELTA = 5;
private DrawOval drawOval = new DrawOval();
public MoveCircle() {
JButton moveRightBtn = new JButton("Move Right");
moveRightBtn.addActionListener(e -> {
// get and update the x position
int x = drawOval.getPositionX();
x += DELTA;
// call the setter method
drawOval.setPositionX(x);
// request that Java repaint the JPanel
drawOval.repaint();
});
JPanel buttonPanel = new JPanel();
buttonPanel.add(moveRightBtn);
setLayout(new BorderLayout());
add(drawOval);
add(buttonPanel, BorderLayout.LINE_START);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(() -> {
MoveCircle mainPanel = new MoveCircle();
JFrame frame = new JFrame("GUI");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(mainPanel);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
});
}
}
#SuppressWarnings("serial")
class DrawOval extends JPanel {
private static final int RADIUS = 100;
private static final int PANEL_WIDTH = 600;
private static final int PANEL_HEIGHT = 450;
private static final Color OVAL_COLOR = Color.RED;
private int positionX = 0;
private int positionY = 0;
public DrawOval() {
setPreferredSize(new Dimension(PANEL_WIDTH, PANEL_HEIGHT));
}
public int getPositionX() {
return positionX;
}
public void setPositionX(int positionX) {
this.positionX = positionX;
}
public int getPositionY() {
return positionY;
}
public void setPositionY(int positionY) {
this.positionY = positionY;
}
#Override
protected void paintComponent(Graphics g) {
// this is needed to do house-keeping painting, to clear "dirty" pixels
super.paintComponent(g);
// this is needed to draw smooth graphics
Graphics2D g2 = (Graphics2D) g;
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
g2.setColor(OVAL_COLOR);
g2.fillOval(positionX, positionY, RADIUS, RADIUS);
}
}

what is Alternative of Paint and repaint function?

Is there any function which can be replaced with paint() and repaint()in java.
I have a scenario.
There is a triangle (Triangle 1). when user will click in triangle another triangle (Triangle 2) will appear and 1st (Triangle 1) will be removed from screen. (coded using JFrame, paint() and repaint())
I have achieved it so far. but problem is when I minimize or change size of window with mouse the output window, it just paint again Triangle 1 rather than Triangle 2. OR Clear the whole screen if i call g2d.clearRect(0, 0, 1000, 1000);
triangle.reset();
Note: These both functions are to remove previous triangle (Triangle 1).
Is there any function that state should not be changed on minimize or when window size changed ?
or can we override repaint() or anything helping according to scenario.
Here is the Working code. Execute it, Click in triangle then minimize and see again. You will get the problem more clearly.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Triangle_shape extends JFrame implements ActionListener {
public static JButton btnSubmit = new JButton("Submit");
public Triangle_shape() {
}
public static void main(String[] args) {
JFrame frame = new JFrame();
frame.setExtendedState(JFrame.MAXIMIZED_BOTH);
frame.setLayout(new BorderLayout());
frame.add(new TrianglePanel(), BorderLayout.CENTER);
frame.add(btnSubmit, BorderLayout.PAGE_END);
frame.pack();
frame.repaint();
frame.setTitle("A Test Frame");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
#Override
public void actionPerformed(ActionEvent e) {
throw new UnsupportedOperationException("Not supported yet.");
}
public static class TrianglePanel extends JPanel implements MouseListener {
private Polygon triangle, triangle2;
public TrianglePanel() {
//Create triangle
triangle = new Polygon();
triangle.addPoint(400, 550); //left
triangle.addPoint(600, 550); //right
triangle.addPoint(500, 350); //top
//Add mouse Listener
addMouseListener(this);
//Set size to make sure that the whole triangle is shown
setPreferredSize(new Dimension(300, 300));
}
/**
* Draws the triangle as this frame's painting
*/
#Override
public void paintComponent(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
g2d.draw(triangle);
}
//Required methods for MouseListener, though the only one you care about is click
public void mousePressed(MouseEvent e) {
}
public void mouseReleased(MouseEvent e) {
}
public void mouseEntered(MouseEvent e) {
}
public void mouseExited(MouseEvent e) {
}
/**
* Called whenever the mouse clicks. Could be replaced with setting the
* value of a JLabel, etc.
*/
public void mouseClicked(MouseEvent e) {
Graphics2D g2d = (Graphics2D) this.getGraphics();
Point p = e.getPoint();
if (triangle.contains(p)) {
System.out.println("1");
g2d.clearRect(0, 0, 1000, 1000);
triangle.reset();
g2d.setColor(Color.MAGENTA);
triangle2 = new Polygon();
triangle2.addPoint(600, 550); // left
triangle2.addPoint(700, 350); //top
triangle2.addPoint(800, 550); //right
g2d.draw(triangle2);
} else {
System.out.println("Triangle dont have point");
}
}
}
}

paint() and repaint() work fine, but you are not using them as they are designed to be used. The window system doesn't keep a persistent image of what a component looks like. It expects your component to be able to repaint its entire appearance on demand (such as when the window is resized or un-minimized).
If you grab a Graphics object with getGraphics() and draw something on the component, the stuff you draw will indeed be lost if/when the entire component needs to be repainted. So you should not do that, but instead make sure your paintComponent method has all the information it needs to completely repaint the component.
If you only want one triangle on the screen at once, do not create a separate variable triangle2. Just replace the one triangle you have by altering your mouse click handler as follows:
public void mouseClicked(MouseEvent e) {
Point p = e.getPoint();
if (triangle.contains(p)) {
triangle = new Polygon();
triangle.addPoint(600, 550); // left
triangle.addPoint(700, 350); //top
triangle.addPoint(800, 550); //right
repaint();
} else {
System.out.println("Point not in triangle");
}
}
Your paintComponent method should call super.paintComponent to ensure the background is painted, but otherwise you do not need to change it:
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D)g;
g2d.draw(triangle);
}
Alternatively if you are trying to keep multiple triangles on the screen, for example, to add a new one at every click, you should add them into a list of shapes which will be drawn whenever the component needs to be repainted:
private final List<Shape> shapes = new ArrayList<>();
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D)g;
for (Shape s : shapes)
g2d.draw(s);
}
Then to control the set of shapes that is on screen, manipulate the contents of the list, and call repaint();.
For instance, to add a new shape to the ones on screen:
Polygon triangle = new Polygon();
triangle.addPoint(200, 300);
triangle.addPoint(200, 200);
triangle.addPoint(300, 200);
shapes.add(triangle);
repaint();
To remove all shapes from the screen:
shapes.clear();
repaint();
You should also make sure that you switch to the Swing thread at the start of the program, because it is not safe to interact with Swing components from the main thread. In main:
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frame = new JFrame();
.
.
.
frame.setVisible(true);
}
});
}

Your mouseClicked method should not create a new Triangle object. After resetting triangle just add new points to it. Also don't draw in this method but call repaint:
public void mouseClicked(MouseEvent e) {
Point p = e.getPoint();
if (triangle.contains(p)) {
System.out.println("1");
triangle.reset(); // change the current triangle
triangle.addPoint(600, 550); // new left
triangle.addPoint(700, 350); // new top
triangle.addPoint(800, 550); // new right
repaint(); // force repainting
} else {
System.out.println("Triangle dont have point");
}
}
Now if you want many triangles you should have a collection of Polygons. Like this :
public static class TrianglePanel extends JPanel implements MouseListener {
private Vector<Polygon> triangles;
public TrianglePanel() {
n = 0;
// Create an empty collection
triangles = new Vector<Polygon>();
//Create first triangle
Polygon triangle = new Polygon();
triangle.addPoint(400, 550); //left
triangle.addPoint(600, 550); //right
triangle.addPoint(500, 350); //top
// Add the triangle to the collection
triangles.add(triangle);
//Add mouse Listener
addMouseListener(this);
//Set size to make sure that the whole triangle is shown
setPreferredSize(new Dimension(300, 300));
}
/**
* Draws the triangles as this frame's painting
*/
#Override
public void paintComponent(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
for (Polygon p : triangles) // Draw all triangles in the collection
g2d.draw(p);
}
//Required methods for MouseListener, though the only one you care about is click
public void mousePressed(MouseEvent e) {}
public void mouseReleased(MouseEvent e) {}
public void mouseEntered(MouseEvent e) {}
public void mouseExited(MouseEvent e) {}
/**
* Called whenever the mouse clicks. Could be replaced with setting the
* value of a JLabel, etc.
*/
public void mouseClicked(MouseEvent e) {
Graphics2D g2d = (Graphics2D) this.getGraphics();
Point p = e.getPoint();
// Do what you want with p and the collection
// For example : remove all triangles that contain the point p
ListIterator<Polygon> li = triangles.listIterator();
while (li.hasNext()) {
if (li.next().contains℗) li.remove();
}
// Do what you want to update the list
// For example: Add a new triangle...
Polygon triangle = new Polygon();
triangle.addPoint(600+n, 550); // left
triangle.addPoint(700+n, 350); //top
triangle.addPoint(800+n, 550); //right
triangles.add(triangle); // add the new triangle to the list
n += 10; // next new triangle will be "moved" right
repaint();
}
private int n;
}

Multi-threaded bouncing balls, issue displaying balls

I'm trying to use multithreading to draw balls that bounce around inside a JFrame. I can get the coordinates of each ball to update and print out, but I can't get the balls to display. I'm not very strong in graphics, and I'm not quite sure what I'm missing. I think I need to add each instance of Ball to the panel I have inside my frame, but when I tried that it didn't make a difference. I also have a class used to view the JFrame, that I've omitted. What am I missing here?
Ball
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.util.Random;
import javax.swing.JPanel;
public class Ball extends JPanel implements Runnable {
JPanel pan;
private static int radius = 10;
private Color color;
private int xPos;
private int yPos;
private int dx;
private int dy;
Dimension d;
public Ball(JPanel p) {
Random r = new Random();
this.pan = p;
this.d = pan.getSize();
xPos = r.nextInt(d.width-50)+25;
yPos = r.nextInt(d.height-50)+25;
dx = r.nextInt(3)+1;
dy = r.nextInt(3)+1;
color = new Color(r.nextInt(255*255*255));
paintComponent(pan.getGraphics());
}
public void move() {
xPos += dx;
yPos += dy;
if (xPos+radius <= 0 || xPos+radius >= d.width)
dx = -dx;
if (yPos+radius <= 0 || yPos+radius >= d.height)
dy = -dy;
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(color);
g.fillOval(xPos-radius, yPos-radius, 2*radius, 2*radius);
g.dispose();
}
public void animate() {
paintComponent(pan.getGraphics());
move();
//pan.validate();//this didn't
//pan.repaint();// work
try {
Thread.sleep(40);
} catch (InterruptedException e) {}
}
public void run() {
while(true)
animate();
}
}
BallTracker
import java.util.ArrayList;
public class BallTracker {
private ArrayList<Ball> balls;
public BallTracker() {
balls = new ArrayList<Ball>();
}
public void addBall(Ball b) {
balls.add(b);
Thread t = new Thread(b);
t.start();
}
}
BallFrame
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class BallFrame extends JFrame {
public static final int WIDTH = 500;
public static final int HEIGHT = 550;
private BallTracker tracker;
private JPanel ballPanel;
private JPanel buttonPanel;
public BallFrame() {
super("BallFrame");
tracker = new BallTracker();
// set up ball panel
ballPanel = new JPanel();
ballPanel.setSize(WIDTH, 500);
// listener to add a new ball to tracker
class bListener implements ActionListener {
public void actionPerformed( ActionEvent event ) {
Ball b = new Ball(ballPanel);
tracker.addBall(b);
}
}
// set up button panel
buttonPanel = new JPanel();
buttonPanel.setSize(WIDTH, 50);
JButton addBallButton = new JButton();
addBallButton.setText("Add ball");
addBallButton.addActionListener(new bListener());
buttonPanel.add(addBallButton);
// add panels to frame
add(buttonPanel, BorderLayout.SOUTH);
add(ballPanel, BorderLayout.CENTER);
setSize( WIDTH, HEIGHT );
}
}

It seems your ball extends jpanel and has a paint method, but your ballPanel would need to do the painting and your ball doesn't really seem to need to be a panel at all.
set up ball panel
ballPanel = new JPanel();
ballPanel.setSize(WIDTH, 500);

I was mainly looking for issues with the way I am trying to draw here, and why I don't see a ball
The Ball isn't added to any panel.
Even when you do add the ball to the panel, the Ball has no size, so there is nothing to paint.
Even if you did give the panel a size only one Ball would ever show up because you Ball panel is opaque.
Your code is attempting to paint the ball at a location within the ball panel. Instead you should be painting the ball at location (0, 0) within your ball panel and then set the location of the Ball panel relative to the parent container.
The parent container should be using a null layout so you can randomly set the location of your Ball panel.
I'm sure there are other issues as well...
I suggest you forget about multithreading and start with the basics of custom painting and using Timers.

Swing: Paint over all other components and preserve events

What I am trying to do: draw a vertical line and a horizontal line that are perpendicular to each other and meet where the mouse points. A sort of cursor tracker.
My structure: JFrame -> CustomPanel -> other panels/components etc.
CustomPanel inherits from JPanel and it's set as my JFrame's ContentPane.
I tried to use a GlassPane, everything worked perfectly, but I want to keep my events, not disable them. I still want to be able to click buttons etc.
A relevant question is this Painting over the top of components in Swing?. Everything behaves as expected when I move my mouse where there are empty places in my CustomPanel, but it still doesn't paint over the other components.
In the image it should have continued painting over the button, but it stopped when I entered it and then resumed when I exited.
Code below.
public class Painter {
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
// TODO code application logic here
JFrame frame = new JFrame();
frame.setSize(600, 600);
frame.setPreferredSize(new Dimension(600, 600));
frame.setContentPane(new CustomPanel());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
class CustomPanel extends JPanel {
int x = 0;
int y = 0;
public CustomPanel() {
addMouseListener(new AdapterImplementation(this));
addMouseMotionListener(new AdapterImplementation(this));
add(new JButton("TESTBTN"));
setSize(new Dimension(600, 600));
setPreferredSize(new Dimension(600, 600));
setVisible(true);
}
#Override
public void paint(Graphics g) {
super.paint(g);
g.drawLine(0, y, getWidth(), y);
g.drawLine(x, 0, x, getHeight());
}
public void setX(int x) {
this.x = x;
}
public void setY(int y) {
this.y = y;
}
}
and my adapter:
public class AdapterImplementation extends MouseAdapter {
CustomPanel pane;
public AdapterImplementation(CustomPanel pane) {
this.pane = pane;
}
#Override
public void mouseDragged(MouseEvent e) {
int x = e.getX();
int y = e.getY();
pane.setX(x);
pane.setY(y);
pane.repaint();
}
#Override
public void mouseMoved(MouseEvent e) {
System.out.println("MOUSE MOVED");
int x = e.getX();
int y = e.getY();
pane.setX(x);
pane.setY(y);
pane.repaint();
}
}

The problem here is that the MouseListeners are registered with your CustomPanel but not with the JButton so the latter does not process events from the listeners.
Also, as you've seen, events to underlying components will be blocked when using GlassPane.
A JLayeredPane could be used to as a topmost container to capture the MouseEvents using your current listeners.
Note: Override paintComponent instead of paint for custom painting in Swing and remember to invoke super.paintComponent(g).
JLayeredPane Example
How to Use Layered Panes

Button inside swing Rectangle2D.double

We have a swing application which displays a lot of rectangles. We use Rectangle2D.double class to draw the rectangles on a JPanel.
My requirement is this. Upon clicking the rectangle, I have to pick an image from the local filesystem and show it in a popup window or a frame.
My question is how can I provide a hyperlink or button inside that Rectangle2D.double rectangle.
Please let me know.
Thanks
-Jad.

I hope this is what you mean:
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.*;
public class RectButton extends JPanel {
Rectangle2D.Double rect;
public RectButton() {
this.addMouseListener(new MouseAdapter() {
public void mouseClicked(MouseEvent e) {
Point point = e.getPoint();
System.out.println(checkRectArea(point));
// Do whatever else you want here.
}
});
}
public boolean checkRectArea(Point point) {
return rect.contains(point);
}
public void paint(Graphics g) {
Graphics2D g2 = (Graphics2D) g;
rect = new Rectangle2D.Double(10, 10, 50, 50);
g2.draw(rect);
}
public static void main(String[] args) {
JFrame frame = new JFrame();
RectButton r = new RectButton();
frame.add(r);
frame.setSize(new Dimension(300, 300));
frame.setVisible(true);
}
}
This program draws a rectangle and print true if you clicked inside the rectangle, false otherwise.

You want to put a MouseListener on the panel, that will catch all clicks anywhere on the panel. You can then get the location of the click from the event and determine which rectangle the click happened in, and then call up the code appropriate for that event and location.