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Trying to draw to a window in JFrame is not exactly working

I'm trying to draw a rectangle to the screen based on mouse listeners. I'm having a few problems:
To start with the shape, it has an offset by a few pixels relative to the
release location of the mouse.
Secondly I can get only the shape to display if I set the screen to
visible each time after adding a JPanel component.
Could anyone tell me what I'm doing wrong or point me in the direction of some documentation? (I’ve read the Oracle documentation but I didn’t really understand it)
I know this isnt the greatest code but i just want to get it working for the moment.
This is my first time asking a question on stackoverflow so if I'm doing something wrong pls tell me.
This is my code
public class Frame {
private JFrame frame;
public Frame() {
this.frame = frameSetup("Graph");
this.frame.addMouseListener(new Mouse());
}
private JFrame frameSetup(String heading) {
JFrame f = new JFrame(heading);
f.setBackground(Color.WHITE);
f.setSize(800, 800);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setLocationRelativeTo(null);
f.setVisible(true);
return f;
}
public void draw(int xIn, int yIn, int widthIn, int heightIn) {
int x = xIn;
int y = yIn;
int width = widthIn;
int height = heightIn;
this.frame.add(new Panel(x, y, width, height));
this.frame.pack();
//this.frame.setVisible(true);
}
private class Mouse implements MouseListener {
int x = 0;
int y = 0;
int height = 0;
int width = 0;
#Override
public void mouseClicked(MouseEvent e) {
}
#Override
public void mousePressed(MouseEvent e) {
if (e.getButton() == 1) {
x = e.getX();
y = e.getY();
System.out.println(x + ": " + y);
}
}
#Override
public void mouseReleased(MouseEvent e) {
if (e.getButton() == 1) {
width = (e.getX() - x);
height = (e.getY() - y);
System.out.println(width + ": " + height);
draw(x - 7, y -30, width, height);
}
}
#Override
public void mouseEntered(MouseEvent e) {
}
#Override
public void mouseExited(MouseEvent e) {
}
}
}
and
public class Panel extends JPanel {
private int x;
private int y;
private int width;
private int height;
public Panel(int x, int y, int width, int height) {
this.x = x;
this.y = y;
this.width = width;
this.height = height;
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.BLACK);
g.fillRect(x, y, width, height);
}
}

Welcome to the Site!
The offset is something I've had plenty of trouble with in the past aswell. It's caused by adding the MouseListener to the JFrame rather than it's contentPane. Basically, the JFrame is the thin border and the bar with the name, the icons and the buttons at the top. The content pane sits inside that, here it's the white surface. When you add the MouseListener to the JFrame, the coords are relative to this outline (the top left corner of the frame), rather than the white panel. This is fixed as follows:
// in the Frame constructor
this.frame.getContentPane().addMouseListener(new Mouse());
// in Mouse.mouseReleased(), remove the offset you added.
draw(x, y, width, height);
The Panel problem is a different story. I don't know how the code is doing what it does or how it works at all in the first place, but I can still give you some general tips.
Don't pack() the frame in the drawing method. It's used to calculate the window size while respecting the layout and the content of it. For me, it made the window as small as the OS allowed it to be.
Don't use JPanels like that! You'll run into weird problems like this, since they're made to be used in GUIs. For this reason, they're also way to heavy-weight to be used as a graphic. #user16320675 commented a tutorial on custom painting, I suggest you check that out.
Lastly, I suggest reworking the rectangle drawing. Right now, it only works when dragging from the top left to the bottom right.

Draw circles that are created as instances in Java GUI

So I've been stuck on this problem for a while now and I'm desperate for help. Please help me. I've got 3 classes:
Circle is just suppose to draw a circle in the frame created by Frame with random starting position (and defind the radius).
Frame is the mainclass with methods such as addCircle(), bounce(), start(), stop(), run() (moves the circles) and quit(). This class also creates the frame in which the circles are added to.
Interfa is just for now a inteface frame where I define the radius, number of circles and Frame size.
No matter what I try I cannot add more than two circle (one is colored and one is not):
The "recursive way":
private static void addCircle(int n){
Circle[] circles = new Circle[n+10];
if (n > 0){
circles[circleAdd] = new Circle();
frame.add(circles[circleAdd]);
circleAdd = circleAdd + 1;
addCircle(n-1);
}
}
Normal itterative way
private static void addCircles(int n){
ArrayList<Circle> circles = new ArrayList<Circle>();
for(int i = 0; i<=n;i++){
circles.add(new Circle());
frame.add(circles.get(i));
}
}
This is how I create my Frame:
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
public Class Frame{
private static JFrame frame;
private static int circleAdd = 0;
private static JPanel fra;
public static void mainFrame(){
frame = new JFrame();
frame.setSize(500,500);
frame.setVisible(true);
fra = new JPanel();
frame.add(fra);
...
//addCircle and addCircles
...
public static void main..
}
}
This is my circle:
import java.awt.*;
import javax.swing.*;
import java.util.Random;
public class Circle extends JPanel{
private Random random = new Random();
public void paint(Graphics g){
int randX = random.nextInt(250)+50;
int randY = random.nextInt(250)+50;
g.drawOval(randX,randY,50,50);
g.setColor(Color.ORANGE);
g.fillOval(100,100,50,50);
}
}

I would suggest that your general approach is wrong. Instead of using a JPanel as the element, you should have a JPanel capable of painting any number of "circles". The Graphics2D API is capable of drawing complex shapes (including ovals).
The main issues I can see are:
JFrame by default is using a BorderLayout, this only allows a single component to be placed in each of the five available positions
Layout managers rely on the preferred/minimum/maximumSize hints to make determinations about the size of the components. They are also responsible for deciding on where the component should be placed. In your current implementation, this would mean that it's possible for you to paint beyond the visible range of the component
Overriding paint is not recommend, and failing to call super.paint could cause a number of unexpected and difficult to diagnose issues
Painting can occur at any time, so using random values in the paint method will cause the UI to constantly change
Instead, you could define your own Circle class which takes the location and size you want and simply acts as a container
public class Circle {
private int x;
private int y;
private int radius;
private Ellipse2D shape;
public Circle(int x, int y, int radius) {
this.x = x;
this.y = y;
this.radius = radius;
this.shape = new Ellipse2D.Double(x, y, radius * 2, radius * 2);
}
public int getX() {
return x;
}
public int getY() {
return y;
}
public int getRadius() {
return radius;
}
public Rectangle getBounds() {
return shape.getBounds();
}
public void paint(Graphics2D g2d) {
g2d.setColor(Color.ORANGE);
g2d.fill(shape);
}
}
This is simply a container class, it represents the information need to generate the desired outcome. It has a convince method which is capable of then painting the shape itself.
You would then need to create a List of these shapes and paint them to your component
public class TestPane extends JPanel {
private List<Circle> circles = new ArrayList<>(10);
private Dimension size;
public TestPane() {
Random random = new Random();
int maxX = 0;
int maxY = 0;
for (int index = 0; index < 10; index++) {
int randX = random.nextInt(250) + 50;
int randY = random.nextInt(250) + 50;
circles.add(new Circle(randX, randY, 25));
maxX = Math.max(maxX, randX + 50);
maxY = Math.max(maxY, randY + 50);
}
size = new Dimension(maxX, maxY);
}
#Override
public Dimension getPreferredSize() {
return size;
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
for (Circle circle : circles) {
Graphics2D g2d = (Graphics2D) g.create();
circle.paint(g2d);
g2d.dispose();
}
}
}
One of the things you seem to lack understanding in is how painting actually works in Swing.
Start by having a look at Performing Custom Painting and Painting in AWT and Swing for more details.
A deeper understanding of how layout managers and the component hierarchy work also wouldn't hurt

How to multithread with paintComponent()?

I created an app that contains a square that bounces every time it touches an edge of the frame.I don't have issues lunching the app,the problem is that i don't know how to create various threads in order to have multiples squares inside the frame.
I tried multiple things but i can't figure out where i should create the threads.
I also noticed that the square is visible only when i add it directly inside the frame and not when i put it inside a JPanel.
Square.java
public class Square extends JComponent implements ActionListener {
int width = 20;
int height = 20;
double y = Math.random() * 360;
double x = Math.random() * 360;
boolean xMax = false;
boolean yMax = false;
boolean xMin = true;
boolean yMin = true;
Rectangle2D.Double square = new Rectangle2D.Double(x, y, width, height);
public Square() {
Timer t = new Timer(2, this);
t.start();
}
public void paintComponent(Graphics g) {
Graphics2D g2 = (Graphics2D) g;
super.paintComponent(g);
g2.setColor(Color.BLUE);
g2.fill(square);
x_y_rules();
}
public void x_y_rules() {
if (xMax == true) {
x = x - 0.5;
if (x <= 0) {
xMax = false;
}
} else {
x = x + 0.5;
if (x >= this.getWidth()) {
xMax = true;
}
}
if (yMax == true) {
y = y - 0.5;
if (y <= 0) {
yMax = false;
}
} else {
y = y + 0.5;
if (y >= this.getHeight()) {
yMax = true;
}
}
square.setFrame(x, y, width, height);
}
#Override
public void actionPerformed(ActionEvent arg0) {
repaint();
}
}
App.java
public class App extends JFrame {
public static void main(String[] args) {
JFrame jf = new JFrame();
Square sqr = new Square();
jf.setSize(400, 400);
jf.setVisible(true);
jf.add(sqr);
jf.setDefaultCloseOperation(EXIT_ON_CLOSE);
jf.setLocationRelativeTo(null);
}
}
Is it normal that despite i put a time of 2 inside the Timer,the square moves very slowly?

Issues:
you've got program logic, the x_y_rules() method call, inside of the paintComponent method. Get it out as it does not belong there, and instead put it into the Timer's ActionListener code where it belongs.
you can give each Square its own Swing Timer if you want. This isn't really a threading issue since each Timer's ActionListener will run on the EDT.
Two milliseconds is an unrealistic time slice to expect to use in a Swing Timer and no timer will run that fast. 11 to 13 is about the fastest to expect or hope for.
if you want your sprite to move faster, give it a greater value for delta-x and delta-y in your movement code.
Your JComponent has no preferred size defined which is likely why it's not showing up in the JPanel, since the default FlowLayout will size it then to [0, 0]. Override its getPreferredSize() and have it return a reasonable Dimension value.
you're calling setVisible(true) on your JFrame before adding all components, a no-no.
Ok,i put a getPrefferedSize() inside the square class but i've encountered a problem: the squares are not "together",it's like they're bouncing on separate panels
Then your program structure is broken. You really don't want create separate Swing components, and in fact your Square class shouldn't extend JComponent or JPanel. Rather
Square should be a logical class, one that extends from nothing (other than default Object).
Give it a drawing method, say public void draw(Graphics g) {....}
Create one class that extends JPanel, say called DrawingPanel, and override its paintComponent method.
Give the DrawingPanel class an ArrayList<Square> so that it can hold multiple Square objects.
Give the DrawingPanel class a Swing Timer
In the DrawingPanel class's Timer, have it update the position of all the Squares in the ArrayList, and then call repaint()
In the paintComponent method, iterate through all the Squares in the list, using a for loop, and call each one's draw method.
For example:
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.util.ArrayList;
import java.util.List;
import javax.swing.*;
#SuppressWarnings("serial")
public class DrawingPanel extends JPanel {
private static final int PREF_W = 600;
private static final int PREF_H = PREF_W;
private static final int TIMER_DELAY = 20;
private static final Color[] SQUARE_COLOR = { Color.BLUE, Color.CYAN, Color.DARK_GRAY,
Color.BLACK, Color.GRAY, Color.GREEN, Color.LIGHT_GRAY, Color.MAGENTA, Color.ORANGE,
Color.PINK, Color.RED, Color.YELLOW };
List<Square> squareList = new ArrayList<>();
public DrawingPanel() {
// create a bunch of squares
for (int i = 0; i < SQUARE_COLOR.length; i++) {
squareList.add(new Square(SQUARE_COLOR[i], PREF_W, PREF_H));
}
setBackground(Color.WHITE);
// create and start the timer
new Timer(TIMER_DELAY, new TimerListener()).start();
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
// simply draw all the squares in the list
for (Square square : squareList) {
square.draw(g);
}
}
// set size of JPanel
#Override
public Dimension getPreferredSize() {
if (isPreferredSizeSet()) {
return super.getPreferredSize();
}
return new Dimension(PREF_W, PREF_H);
}
private class TimerListener implements ActionListener {
#Override
public void actionPerformed(ActionEvent e) {
// simply iterate through list and move all squares
for (Square square : squareList) {
square.move();
}
repaint(); // then repaint the GUI
}
}
private static void createAndShowGui() {
DrawingPanel mainPanel = new DrawingPanel();
JFrame frame = new JFrame("Drawing Panel");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(() -> createAndShowGui());
}
}
// this class does *not* extend JPanel or JComponent
class Square {
public static final int WIDTH = 20;
// location of Square
private double sqrX;
private double sqrY;
// X and Y speed
private double deltaX;
private double deltaY;
// width and height of DrawingPanel JPanel
private int dpWidth;
private int dpHeight;
// image to draw
private Image image;
public Square(Color color, int dpWidth, int dpHeight) {
this.dpWidth = dpWidth;
this.dpHeight = dpHeight;
// create square at random location with random speed
sqrX = Math.random() * (dpWidth - WIDTH);
sqrY = Math.random() * (dpHeight - WIDTH);
deltaX = Math.random() * 10 - 5;
deltaY = Math.random() * 10 - 5;
// one way to draw it is to create an image and draw it
image = new BufferedImage(WIDTH, WIDTH, BufferedImage.TYPE_INT_ARGB);
Graphics g = image.getGraphics();
g.setColor(color);
g.fillRect(0, 0, WIDTH, WIDTH);
g.dispose();
}
public void move() {
// check that we're not hitting boundaries
if (sqrX + deltaX < 0) {
deltaX = Math.abs(deltaX);
}
if (sqrX + deltaX + WIDTH >= dpWidth) {
deltaX = -Math.abs(deltaX);
}
sqrX += deltaX;
// check that we're not hitting boundaries
if (sqrY + deltaY < 0) {
deltaY = Math.abs(deltaY);
}
if (sqrY + deltaY + WIDTH >= dpHeight) {
deltaY = -Math.abs(deltaY);
}
sqrY += deltaY;
}
public void draw(Graphics g) {
int x = (int) sqrX;
int y = (int) sqrY;
g.drawImage(image, x, y, null);
}
}

Java hit-test behaving strangely

I was trying to extend the java ScrollDemo2 to report if a shape on the canvas had been clicked. I started with a simple rectangle believing that it should be no problem to simply loop over rectangle in the canvas checking if the click point was contained within them. But then something peculiar happened, the contains methods only seems to care if the point is in a rectangle anchored at (0,0), and doesn't seem to care that my component is at y=20. Therefore i get a hit if I click withing the Jpanel from x:[0,20] y:[0,20] when I should only get a hit if I click on x:[0,20] y[20,40]. Is this a bug, or am I doing something incorrectly?
public class CachedDrawableComponent extends JComponent
{
//this will do more later
CachedDrawableComponent(Rectangle bounds)
{
this.setBounds(bounds);
}
protected void paintComponent(Graphics g)
{
g.setColor(Color.magenta);
Rectangle r = this.getBounds();
g.fillRect(r.x, r.y, r.width, r.height);
}
}
public class ScrollDemo2 extends JPanel
implements MouseListener {
private Dimension area; //indicates area taken up by graphics
private Vector<Rectangle> circles; //coordinates used to draw graphics
private Vector<CachedDrawableComponent> otherDrawables;
private JPanel drawingPane;
private final Color colors[] = {
Color.red, Color.blue, Color.green, Color.orange,
Color.cyan, Color.magenta, Color.darkGray, Color.yellow};
private final int color_n = colors.length;
public ScrollDemo2() {
super(new BorderLayout());
area = new Dimension(0,0);
circles = new Vector<Rectangle>();
this.otherDrawables = new Vector<CachedDrawableComponent>();
//Set up the instructions.
JLabel instructionsLeft = new JLabel(
"Click left mouse button to place a circle.");
JLabel instructionsRight = new JLabel(
"Click right mouse button to clear drawing area.");
JPanel instructionPanel = new JPanel(new GridLayout(0,1));
instructionPanel.setFocusable(true);
instructionPanel.add(instructionsLeft);
instructionPanel.add(instructionsRight);
//Set up the drawing area.
drawingPane = new DrawingPane();
drawingPane.setBackground(Color.white);
drawingPane.addMouseListener(this);
TestRect t = new TestRect(new Rectangle(0,20,20,20));
this.otherDrawables.add(t);
//Put the drawing area in a scroll pane.
JScrollPane scroller = new JScrollPane(drawingPane);
scroller.setPreferredSize(new Dimension(200,200));
//Lay out this demo.
add(instructionPanel, BorderLayout.PAGE_START);
add(scroller, BorderLayout.CENTER);
}
/** The component inside the scroll pane. */
public class DrawingPane extends JPanel {
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Rectangle rect;
for (int i = 0; i < circles.size(); i++) {
rect = circles.elementAt(i);
g.setColor(colors[(i % color_n)]);
g.fillOval(rect.x, rect.y, rect.width, rect.height);
}
for (int i = 0; i < otherDrawables.size(); i++) {
CachedDrawableComponent drawMe = otherDrawables.elementAt(i);;
g.setColor(colors[(i % color_n)]);
drawMe.paint(g);
}
}
}
//Handle mouse events.
public void mouseReleased(MouseEvent e) {
final int W = 100;
final int H = 100;
boolean changed = false;
if (SwingUtilities.isRightMouseButton(e)) {
//This will clear the graphic objects.
circles.removeAllElements();
area.width=0;
area.height=0;
changed = true;
} else {
int x = e.getX() - W/2;
int y = e.getY() - H/2;
if (x < 0) x = 0;
if (y < 0) y = 0;
Rectangle rect = new Rectangle(x, y, W, H);
circles.addElement(rect);
drawingPane.scrollRectToVisible(rect);
int this_width = (x + W + 2);
if (this_width > area.width) {
area.width = this_width; changed=true;
}
int this_height = (y + H + 2);
if (this_height > area.height) {
area.height = this_height; changed=true;
}
}
if (changed) {
//Update client's preferred size because
//the area taken up by the graphics has
//gotten larger or smaller (if cleared).
drawingPane.setPreferredSize(area);
//Let the scroll pane know to update itself
//and its scrollbars.
drawingPane.revalidate();
}
drawingPane.repaint();
}
public void mouseClicked(MouseEvent e){}
public void mouseEntered(MouseEvent e){}
public void mouseExited(MouseEvent e){}
public void mousePressed(MouseEvent e)
{
System.out.println("Did press:"+e.getPoint());
System.out.println(otherDrawables.get(0).getBounds());
if(otherDrawables.get(0).contains(e.getPoint()))
{
System.out.println("Did Hit");
}
}
/**
* Create the GUI and show it. For thread safety,
* this method should be invoked from the
* event-dispatching thread.
*/
private static void createAndShowGUI() {
//Create and set up the window.
JFrame frame = new JFrame("ScrollDemo2");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Create and set up the content pane.
JComponent newContentPane = new ScrollDemo2();
newContentPane.setOpaque(true); //content panes must be opaque
frame.setContentPane(newContentPane);
//Display the window.
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
//Schedule a job for the event-dispatching thread:
//creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}
Output:
Did press:java.awt.Point[x=8,y=7]
java.awt.Rectangle[x=0,y=20,width=20,height=20]
Did Hit
Did press:java.awt.Point[x=14,y=89]
java.awt.Rectangle[x=0,y=20,width=20,height=20]

The face problem is that you are mixing coordinate systems:
the coordinates in the mouseListener are coordinates of the drawingPane
the coordinates expected in somecomponent.contains are coordinates of the component
From the api doc of contains:
Checks whether this component "contains" the specified point,
where x and y are defined to be
relative to the coordinate system of this component.
It's unusual (don't do without a reeeaal good reason :-) to have those components without actually adding them to the drawingPane.

Check out Playing With Shapes. It may give you some ideas for a slightly different approach.
For example by creating Shapes you don't need to keep track of Rectangle and others since all shapes will be treated the same.
You can also use the Shapes as components is you wish.

add 2 objects to JFrame on a specific location

This is my class that creates a circle shape with specific x and y coordinates. Similarly I have another same class but with different x and y coordinate positions. I create 1 object of each class and want to display them on specific positions on JFrame.When I add 2nd object to JFrmae, it overwrites the 1st object. I tried with different layouts of JFrmae but it did not work.
class Ballbewegung2 extends JPanel implements Runnable {
int x_pos = 10; int y_pos = 100; int radius = 20;
public void init() {
setBackground (Color.blue); }
public void start () {
Thread th = new Thread (this);
th.start (); }
public void run () {
Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
while (true) {
x_pos ++; if(x_pos >= 400) x_pos = 10;
repaint();
try { Thread.sleep (20); }
catch (InterruptedException ex) {} thread.currentThread().setPriority(Thread.MAX_
PRIORITY); } } public void paint (Graphics g) { g.setColor (Color.red); g.fillOval (x_pos - radius, y_pos - radius, 2 * radius, 2 * radius); } }

If you make the layout of the JFrame null, you will be able to explicitly control the position of any component that you add. Also make sure that you are adding to the content pane of the JFrame.