Develop Reference

How do I make a graphics change place randomly everytime I click on it

The code I made won't change the coordinates of the ball every time I click on it.
public class AimTrainerPanel extends JPanel implements MouseListener {
static final int WIDTH = 1300;
static final int HEIGHT = 750;
static final int SIZE = 10;
Random rand;
JLabel cd;
int x;
int y;
boolean running = false;
Timer timer;
AimTrainerPanel() {
rand = new Random();
this.setPreferredSize(new Dimension(WIDTH, HEIGHT));
this.setBackground(Color.black);
this.setFocusable(true);
this.setLayout(null);
this.addMouseListener(this);
startGame();
}
public void startGame() {
newDot();
running = true;
timer = new Timer();
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
draw(g);
}
public void draw(Graphics g) {
if (running) {
g.setColor(Color.white);
g.fillOval(x, y, SIZE, SIZE);
}
}
public void newDot() {
x = rand.nextInt((int)(WIDTH/SIZE)) * SIZE;
y = rand.nextInt((int)(HEIGHT/SIZE)) * SIZE;
}
#Override
public void mouseClicked(MouseEvent e) {
int mx = e.getX();
int my = e.getY();
if (mx >= x && mx <= x + 10) {
if (my >= y && my <= y + 10) {
newDot();
}
}
}
#Override
public void mousePressed(MouseEvent e) {
}
#Override
public void mouseReleased(MouseEvent e) {
}
#Override
public void mouseEntered(MouseEvent e) {
}
#Override
public void mouseExited(MouseEvent e) {
}
}
The newDot() method is suppose to create new coordinates every time it is called but the ball won't change places. I don't know if it's because I misswrote something or because my what I did doesn't change the coordinates or if I'm suppose to add something.

I'm not sure what your Timer is supposed to be doing, but it doesn't appear to be a Swing Timer, and since this is a Swing GUI I'd get rid of it.
Now to the crux of your problems:
You're using mouseClicked which isn't called if the mouse moves even slightly between mouse pressed and mouse released, and so often it is better to use mousePressed or mouseReleased methods and not mouseClicked
You don't call repaint() after changing the state of your program. Swing won't know that a repaint is needed unless you suggested, and so in your mouseListener or in code called by it, you should call this method after changing GUI state. Here you can call it at the end of the newDot(...) method or in the mouse listener after you call the same method.
Your if blocks within your mouse listener appear to be quite restrictive as to where they will allow the listener to respond to a mouse click -- is it too restrictive? I don't know since I'm not familiar with your requirements, but possibly.

Paint method not painting Java

My paint method doesnt seem to paint my 20x20 cells. I have a boolean array for the cells to control their state and that if true, call the cells paint method, a cell is painted however I have two problems;
Only one is painted at a time which is odd because i should have a 40x40 array of booleans meaning i have 40x40 cells
They dont actually paint exactly where I click. I do not know how this is the case as when I get the co-ordinates of my click I immediately place those co-ordinates as my x, and y values in my paint method.
Main
import javax.swing.*;
import java.awt.*;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.image.BufferStrategy;
public class mainApplication extends JFrame implements Runnable, MouseListener {
private static final Dimension windowsize = new Dimension(80, 600);
private BufferStrategy strategy;
private Graphics offscreenGraphics;
private static boolean isGraphicsInitialised = false;
private static int rows = 40;
private static int columns = 40;
private static int height = windowsize.height;
private static int width = windowsize.width;
private static Cells cells = new Cells();
private int xArrayElement,yArrayElement, xPosition, yPosition;
private static boolean gameState[][] = new boolean[rows][columns];
public mainApplication() {
System.out.println(System.getProperty("user.dir"));
setDefaultCloseOperation(EXIT_ON_CLOSE);
Dimension screensize = java.awt.Toolkit.getDefaultToolkit().getScreenSize();
int x = screensize.width / 2 - windowsize.width / 2;
int y = screensize.height / 2 - windowsize.height / 2;
setBounds(x, y, screensize.width, screensize.height);
setVisible(true);
createBufferStrategy(2);
strategy = getBufferStrategy();
offscreenGraphics = strategy.getDrawGraphics();
isGraphicsInitialised = true;
// MouseEvent mouseEvent = new MouseEvent();
addMouseListener(this);
// addMouseMotionListener(MouseEvent);
Thread t = new Thread(this);
t.start();
}
public void mousePressed(MouseEvent e) { }
public void mouseReleased(MouseEvent e) { }
public void mouseEntered(MouseEvent e) { }
public void mouseExited(MouseEvent e) { }
public void mouseClicked(MouseEvent e) {
if(e.getClickCount() == 1){
xPosition = e.getX();
yPosition = e.getY();
cells.setPosition(xPosition,yPosition);
xArrayElement = (xPosition/20);
yArrayElement = (yPosition/20);
if(gameState[xArrayElement][yArrayElement]){
gameState[xArrayElement][yArrayElement] = false;
}
else if (!gameState[xArrayElement][yArrayElement]) {
gameState[xArrayElement][yArrayElement] = true;
}
else(gameState[xArrayElement][yArrayElement]) = true;
}
}
#Override
public void run() {
while (true) {
try { //threads entry point
Thread.sleep(20); //forces us to catch exception
}
catch (InterruptedException e) {
}
this.repaint();
}
}
public void paint(Graphics g) {
if (isGraphicsInitialised) {
g = strategy.getDrawGraphics();
g.setColor(Color.BLACK);
g.fillRect(0, 0, 800, 800);
if (gameState[xArrayElement][yArrayElement]) {
g.setColor(Color.WHITE);
cells.paint(g);
System.out.println(xPosition);
}
else if (!gameState[xArrayElement][yArrayElement]) {
g.setColor(Color.BLACK);
g.fillRect(xPosition, yPosition, 20, 20);
}
strategy.show();
}
}
public static void main(String[]args){
mainApplication test = new mainApplication();
}
}
Cell Class
import java.awt.*;
public class Cells {
int x;
int y;
public Cells(){
}
public void setPosition(int xi, int xj){
x = xi;
y = xi;
}
public boolean cellState(boolean visible){
return visible;
}
public void paint(Graphics g){
g.drawRect(x, y, 20,20);
}
}

You are doing a number of things wrong. My first suggestion would be to forget about offscreen graphics and ensure you are doing what you want. You can always create an image latter. Here are some basic guidelines:
Don't extend JFrame. Use an instance.
Extend JPanel or create a class that extends JPanel and add to frame instance
Then override paintComponent(g) and use that graphics context to draw.
Here is an earlier answer that may help Can't add Graphics into JPanel in Java
More information may be found in the Java Tutorials on painting.
Updated. It took me a few minutes to find this.
public void setPosition(int xi, int xj){
x = xi;
y = xi; // <--- should be xj
}
Regarding (1) above. You must repaint every cell each time you enter paintComponent. This means you will need to iterate across the list and paint them in the correct spot. Right now you are only painting one upon each entry.
A couple more suggestions. Instead of messing with the thread and calling repaint every 20ms in a loop, why not just invoke repaint in the mouseClicked() method.
If you do eventually need to paint every 20ms. I suggest using a swing Timer as follows: (check JavaDoc to ensure I got the syntax correct!!)
Timer timer = new Timer(0, (ev)-> frame.repaint());
timer.setDelay(20);
timer.start();
And you can create your own mouseListener class and extending MouseAdapter. The purpose of these adapter classes is to keep the clutter down so you don't have to have empty methods to satisfy the interface requirements. Put the class inside your main class so it has access to the appropriate data structures. Then just add an instance of it to the mouse listener of the target Component.

Oval on JPanel won't draw on different locations

I have a panel on which I have to draw balls, each time I press the mouse button. The balls are supposed to be drawn on the location pressed by the mouse.
The balls are drawn just fine, however they are drawn on the same location every time, so unless I "move" the window right and left, the drawn balls would not be seen.
Here's my code:
GUIBalls
public class GUIBalls {
public JFrame frame = new JFrame("Balls");
public JPanel panel = new JPanel();
private ArrayList<Ball> b = new ArrayList<>();
private Random rnd = new Random();
public GUIBalls(){
setFrame();
//moveBalls();
}
public void setFrame(){
this.frame.setBounds(0,0,400,400);
this.frame.add(panel);
panel.setBounds(0,0,400,400);
this.panel.addMouseListener(new MouseListener() {
#Override
public void mouseClicked(MouseEvent e) {
}
#Override
public void mousePressed(MouseEvent e) {
int x = e.getX();
int y = e.getY();
createBalls(x,y);
}
#Override
public void mouseReleased(MouseEvent e) {
}
#Override
public void mouseEntered(MouseEvent e) {
}
#Override
public void mouseExited(MouseEvent e) {
}
});
}
public void createBalls(int x, int y){
Ball ball = new Ball(x,y,10,10);
this.b.add(ball);
ball.draw(panel);
panel.repaint();
}
}
Ball
public class Ball extends JPanel {
int x;
int y;
int z;
int w;
public Ball(int x, int y, int z, int w) {
this.x = x;
this.y = y;
this.z = z;
this.w = w;
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.fillOval(0, 0, z, w);
}
public void draw(JPanel panel) {
panel.add(this);
panel.setVisible(true);
}
}
For some odd reason, the balls are not being drawn on different locations.
Pictures of what happens are attached.
Any Ideas?

The problem with your code right now is that you have a combination of trying to do custom painting and trying to create a custom component. You need to decide which approach you want to use.
For the basics of custom painting read the section from the Swing tutorial on Custom Painting that has a working example showing how to do this. Well, it shows how to draw a square on a panel but you get the idea.
If you want to keep adding objects to be painted, then you need to keep your objects in a ArrayList and then in the paintComponent() method you iterate through the List to paint each object. This approach is demonstrated in Custom Painting Approaches.
If you want to create a Ball as a component, then you need to make sure you override the get preferred size to return the size of the Ball. Then you always draw the oval at offset (0, 0) of the panel. You then add the Ball component to the parent panel which uses a null layout. Because you use a null layout you will position the Ball on the parent panel by using the setLocation(...) method. You will also need to use the setSize() method of the Ball component to be the preferred size.

deleting previously clicked rectangle in java for thread [duplicate]

As the title says, I'm having a hard time trying to draw some rectangles (filled) in JApplet.
The exact goal is to have a 50x50 table and when you click on a targeted cell, to make it filled (possibly done by drawing a filled rectangle). I have done the maths about the coordinates of the starting point, but for some reason I can't draw the new rectangle in the MouseClicked method. Any suggestions?
public class Main extends JApplet {
public static final int DIMX = 800;
public static final int DIMY = 800;
public static final int ratio = 16;
Graphics g;
boolean drawing;
public int cX;
public int cY;
public Main() {
JPanel MainFrame = new JPanel();
MainFrame.setPreferredSize(new Dimension(400, 800));
MainFrame.setBackground(Color.LIGHT_GRAY);
JPanel Table = new JPanel();
Table.setPreferredSize(new Dimension(800, 800));
Table.setBackground(Color.LIGHT_GRAY);
add(MainFrame, BorderLayout.EAST);
add(Table, BorderLayout.WEST);
addMouseListener(new clicked());
}
public void paint(Graphics g) {
super.paintComponents(g);
g.setColor(Color.black);
for (int i = 0; i <= 800; i += 16) {
g.drawLine(0, i, 800, i);
g.drawLine(i, 0, i, 800);
// g.fillRect(cX, cY, 16, 16);
}
}
public static void main(String[] args) {
JFrame win = new JFrame("Retarded Bullshit");
win.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
win.setPreferredSize(new Dimension(1216, 840));
win.setContentPane(new Main());
win.pack();
win.setVisible(true);
}
public class clicked extends JApplet implements MouseListener {
public int cX;
public int cY;
Graphics g;
#Override
public void mouseClicked(MouseEvent e) {
// Point a = e.getLocationOnScreen();
int cellX = e.getX();
int cellY = e.getY();
if (cellX < 800 && cellX > 0 && cellY < 800 && cellY > 0) {
cX = cellX / 16 + 1;
cY = cellY / 16 + 1;
JOptionPane.showMessageDialog(null, "" + cX + " " + cY);
}

This is a relatively simple concept (no offense).
To start with, don't mix your code with JApplet and JFrame. If you want to use your application in these two mediums, separate the logic into a separate component (like JPanel) which you can easily add to either. You really shouldn't add a top level container to another top level container (adding an applet to a frame) - it's messy.
Avoid overriding the paint methods of top level containers (like JApplet), instead, use a custom component (like JPanel) instead and override it's paintComponent method.
In your example, you should be calling super.paint rather then super.paintComponents. paint does important work, you don't want to skip it - but you should be using JComponent#paintComponent
MouseListeners should added to the components that you are interested in managing mouse events. Because clicked is never added to any containers, it will never recieve mouse events.
Take a look at
How to write mouse listeners
Performing Custom Painting
2D Graphics
Painting in AWT and Swing (because every Swing developer should have an understanding of this)
public class SimplePaint03 {
public static void main(String[] args) {
new SimplePaint03();
}
public SimplePaint03() {
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.add(new PaintPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class PaintPane extends JPanel {
private List<Shape> grid;
private List<Shape> fill;
public PaintPane() {
grid = new ArrayList<>(5);
fill = new ArrayList<>(5);
addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
for (Shape shape : grid) {
if (shape.contains(e.getPoint())) {
if (fill.contains(shape)) {
fill.remove(shape);
} else {
fill.add(shape);
}
}
}
repaint();
}
});
int colWidth = 200 / 50;
int rowHeight = 200 / 50;
for (int row = 0; row < 50; row++) {
for (int col = 0; col < 50; col++) {
grid.add(new Rectangle(colWidth * col, rowHeight * row, colWidth, rowHeight));
}
}
}
#Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
g2d.setColor(Color.RED);
for (Shape cell : fill) {
g2d.fill(cell);
}
g2d.setColor(Color.BLACK);
for (Shape cell : grid) {
g2d.draw(cell);
}
}
}
}
Additional
Information from one paint cycle to another is not maintained. You are required to repaint the component exactly the way you want it to appear. This means you will need to maintain a list of click points that can be repainted at any time.

Start by reading the Swing tutorial on Custom Painting.
Custom painting is done by overriding the paintComponent() method of a JPanel or JComponent(). Then you add the panel to the JApplet.
If you only want to paint certain squares then you are going to need a List to keep track of which cells to paint. Then every time you repaint the component you will need to loop through the List and paint the cells.
Your MouseListener would not extend JApplet. When you click on a cell you would update the List from above to indicate that the cell needs to be painted. Then you would invoke repaint() on the panel so that your painting code will be invoked.
You may also want to look at Custom Painting Approaches which gives two different ways to do this type of painting depending on your exact requirement.

how to draw rectangle on java applet using mouse drag event

i am using java.
i want to draw rectangle based on mousedrag event. if user dragging the mouse, then the rectangle on the applet should increase or decrease basing on current mouse coordinates.
i have the following code.
in the following code i am using [b]SelectionArea[/b] class which extends a canvas on which i am performing drawing operation. i am using [b]image[/b] variable in this class for double buffering to reduce flickering and to save the applet's previous state(i.e drawing content of applet)
but the code is working fine if i draw first rectangle. if i start to draw second rectangle the previously drawn rectangle is disappearing. i want the previously drawn rectangle to be on the screen
can any one tell me how to solve this.
import java.awt.*;
import java.applet.Applet;
import java.awt.event.*;
/*
* This displays a framed area. When the user drags within
* the area, this program displays a rectangle extending from
* where the user first pressed the mouse button to the current
* cursor location.
*/
public class RectangleDemo extends Applet {
SelectionArea drawingPanel;
Label label;
public void init() {
GridBagLayout gridBag = new GridBagLayout();
GridBagConstraints c = new GridBagConstraints();
setLayout(gridBag);
drawingPanel = new SelectionArea(this);
c.fill = GridBagConstraints.BOTH;
c.weighty = 1.0;
c.gridwidth = GridBagConstraints.REMAINDER; //end row
gridBag.setConstraints(drawingPanel, c);
add(drawingPanel);
label = new Label("Drag within the framed area.");
c.fill = GridBagConstraints.HORIZONTAL;
c.weightx = 1.0;
c.weighty = 0.0;
gridBag.setConstraints(label, c);
add(label);
drawingPanel.setVisible(true);
validate();
}
public void paint(Graphics g){
drawingPanel.repaint();
}
public void update(Graphics g){
paint(g);
}
}
class SelectionArea extends Canvas implements ActionListener, MouseListener, MouseMotionListener{
Rectangle currentRect;
RectangleDemo controller;
//for double buffering
Image image;
Graphics offscreen;
public SelectionArea(RectangleDemo controller) {
super();
this.controller = controller;
addMouseListener(this);
addMouseMotionListener(this);
}
public void actionPerformed(ActionEvent ae){
repaintoffscreen();
}
public void repaintoffscreen(){
image = createImage(this.getWidth(), this.getHeight());
offscreen = image.getGraphics();
Dimension d = getSize();
if(currentRect != null){
Rectangle box = getDrawableRect(currentRect, d);
//Draw the box outline.
offscreen.drawRect(box.x, box.y, box.width - 1, box.height - 1);
//repaint();
}
}
public void mouseEntered(MouseEvent me) {}
public void mouseExited(MouseEvent me){ }
public void mouseClicked(MouseEvent me){}
public void mouseMoved(MouseEvent me){}
public void mousePressed(MouseEvent me) {
currentRect = new Rectangle(me.getX(), me.getY(), 0, 0);
repaintoffscreen();
}
public void mouseDragged(MouseEvent me) {
System.out.println("here in dragged()");
currentRect.setSize(me.getX() - currentRect.x, me.getY() - currentRect.y);
repaintoffscreen();
repaint();
}
public void mouseReleased(MouseEvent me) {
currentRect.setSize(me.getX() - currentRect.x, me.getY() - currentRect.y);
repaintoffscreen();
repaint();
}
public void update(Graphics g){
paint(g);
}
public void paint(Graphics g) {
g.drawImage(image, 0, 0, this);
}
Rectangle getDrawableRect(Rectangle originalRect, Dimension drawingArea) {
int x = originalRect.x;
int y = originalRect.y;
int width = originalRect.width;
int height = originalRect.height;
//Make sure rectangle width and height are positive.
if (width < 0) {
width = 0 - width;
x = x - width + 1;
if (x < 0) {
width += x;
x = 0;
}
}
if (height < 0) {
height = 0 - height;
y = y - height + 1;
if (y < 0) {
height += y;
y = 0;
}
}
//The rectangle shouldn't extend past the drawing area.
if ((x + width) > drawingArea.width) {
width = drawingArea.width - x;
}
if ((y + height) > drawingArea.height) {
height = drawingArea.height - y;
}
return new Rectangle(x, y, width, height);
}
}
also if i run this code on full screen mode then i am seeing that the rectangle is appering on screen only after i released the mouse. but i want the rectangle to be on the screen while dragging the mouse and it should change it's dimension according to the current mouse coordinates.
can any one help me pls.

homework?
basically what you need to do is:
on mouse down keep the mouse-down coordinates and repaint
on mouse move keep current mouse coordinates and repaint
on mouse up, nullify the mouse-down coordinates to indicate there is no rect, and repaint.
on paint, draw background and then rect between mousedown and cur-mouse coordinates.
if you don't want to keep a background image, you can do a trick with the Graphics xor function, drawing the same rect twice will erase the old rect, so you can use it to restore the old image straight on the graphics object.
Edit: code xor usage sample:
public void paint(Graphics g)
{
g.setXORMode(Color.black);
// draw old rect if there is one. this will erase it
// draw new rect, this will draw xored
g.setDrawMode(); // restore normal draw mode
}
Xor has the an interesting property:
xor(xor(x)) = x
so xoring the same pixel twice restores it's original color.

There are a couple issues that need to be addressed.
First, regarding only one rectangle can be drawn, this is due to the design of your program. In your code, whenever the repaintoffscreen method is called, the currectRect field is used to draw a rectangle. However, there is no provision to keep holding onto rectangles which were made in the past.
One way to keep a hold of past rectangles would be perhaps to make another field which is, for example, a List<Rectangle> which is used to store past rectangles. Then, when the mouse is released, add the current rectangle to that list.
Then, in order for all rectangles, currentRect and past rectangles to appear, repaintoffscreen will need to not only perform getDrawableRect and offscreen.drawRect using the currentRect but also with the past rectangles which are stored in the List<Rectangle>. (Hint, use a for loop to iterate through the list.)
Second, regarding the rectangle not appearing until after releasing the mouse button, rather than using the mouseDragged method, maybe using the mouseMoved method along with a check to see that the mouse button is depressed may be a workaround. (I think I've also had trouble dealing with the mouseDragged method in the past.)
The MouseEvent passed into the mouseMoved method can be used to check if a button is depressed by the getButton method:
public void mouseMoved(MouseEvent e)
{
// Check if button1 is pressed.
if (e.getButton() == MouseEvent.BUTTON1)
{
// Perform sizing of rectangle and off-screen drawing, and repaint.
}
}

My question was about create a select rectangle invert mouse click position, but, in the end I got make this with this method:
... //to set the selection area
private int iniSelX;
private int iniSelY;
private int endSelX;
private int endSelY;
private JPanel myJPanel = new JPanel() {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.WHITE);
g.fillRect(0, 0, this.getWidth(), this.getHeight());
g.setColor(Color.red);
g.drawLine(260, 5, 260, 260);
g.setColor(Color.BLUE);
//verify if go draw the rectangle
if (iniSelX != 0 || endSelX != 0) {
boolean revertX = iniSelX < endSelX;
boolean revertY = iniSelY < endSelY;
//Simple way
//g.drawRect(iniSelX, iniSelY, endSelX - iniSelX, endSelY - iniSelY);
//reverse way
g.drawRect(revertX ? iniSelX : endSelX, revertY ? iniSelY : endSelY,
revertX ? endSelX - iniSelX : iniSelX - endSelX, revertY ? endSelY - iniSelY : iniSelY - endSelY);
}
}
}; ...
addMouseMotionListener(new MouseMotionListener() {
#Override
public void mouseDragged(MouseEvent m) {
//update selection area
endSelX = m.getX();
endSelY = m.getY();
repaint();
}
#Override
public void mouseMoved(MouseEvent m) {
repaint();
}
});
addMouseListener(new MouseListener() {
...
#Override
public void mousePressed(MouseEvent e) {
//start drawing the selection
iniSelX = e.getX() - 15;
iniSelY = e.getY() - 20;
}
#Override
public void mouseReleased(MouseEvent e) {
//start drawing the selection
iniSelX = 0;
iniSelY = 0;
endSelX = 0;
endSelY = 0;
}
...
});
}
public void log() {
System.out.println("iniSelX" + iniSelX);
System.out.println("iniSelY" + iniSelY);
System.out.println("endSelX" + endSelX);
System.out.println("endSelY" + endSelY);
} ...
I hope this is useful.