Develop Reference

Multi- threading in Java - trouble with implmenting in program

I created the below bouncing ball program. I'm new to programming in general, but got this working fine. The objective was to have the ball bounce within the frame and to appear in random locations at program start up.
the next thing I am trying to do is to intoduce multiple balls into the frame that bounce around. I'm trying to do this using the Rnnable interface but havent been able to get this working. The Balls can move independently, passing through each other. Each Ball should have its own thread, rather than one thread updating an array of Balls.Below is my attempt but I havent able to get this working.
Any advice would be great.
/*Bounce class*/
import java.awt.Color;
import java.awt.Graphics;
import java.util.concurrent.ThreadLocalRandom;
import javax.swing.JPanel;
public class Bounce2 extends JPanel implements Runnable {
private static final long serialVersionUID = 1L;
/*variables*/
int x, y;
int anglex = 1, angley = 1, speed = 10;
int min = 40, max = 760;
public Bounce2() {
min = 60;
max = 740;
}
public void setGenerateRandom (int max, int min) {
x = ThreadLocalRandom.current().nextInt(min, max +1);
y = ThreadLocalRandom.current().nextInt(min, max +1);
run();
}
public void run() {
if (x + anglex < 0) {
anglex = speed;
} else if (x + anglex > getWidth() - 50) {
anglex = -speed;
} else if (y + angley < 0) {
angley = speed;
} else if (y + angley > getHeight() - 50) {
angley = -speed;
}
x = x + anglex;
y = y + angley;
}
public void paint (Graphics g) {
super.paint(g);
Color c = Color.blue;
g.setColor(c);
g.fillOval(x, y, 80, 80);
}
public void random() {
setGenerateRandom(max, min);
}
}
/*Bounce2Test class*/
import javax.swing.JFrame;
import javax.swing.JOptionPane;
public class Bounce2Test {
public static void main(String[] args) throws InterruptedException {
{
int num = 0;
String objects;
objects = JOptionPane.showInputDialog("Please enter number of balls!");
num = Integer.parseInt(objects);
// Number of threads
for (int i = 0; i < num; i++) {
Thread object = new Thread(new Bounce2());
object.start();
JFrame frame = new JFrame("Bouncing Ball");
Bounce2 ball = new Bounce2();
frame.add(ball);
frame.setSize(800,800);
frame.setVisible(true);
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
ball.random();
while(true) {
ball.run();
ball.repaint();
Thread.sleep(10);
}
}
}
}
}

Java - Hexagon location in grid

Im searching for an algorythem to get the location of a hexagon in a grid.
I found this one but it doesnt seam to work:
for(int i = 0; i < width; i++) {
for(int j = 0; j < height; j++) {
grid[i][j] = new Hexagon(x+(j*((3*Hexagon.S)/2)), y+((j%2)*Hexagon.A)+(2*i*Hexagon.A));
}
}
The output is kind of strange:
output
This is the window-creating class(just a test class):
import java.awt.Container;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Grid extends JPanel {
private static final long serialVersionUID = 1L;
public static void main(String[] args) {
int width = 2;
int height = 4;
int x = 100;
int y = 100;
Hexagon[][] grid = new Hexagon[width][height];
JFrame f = new JFrame();
Container cp = f.getContentPane();
for(int i = 0; i < width; i++) {
for(int j = 0; j < height; j++) {
grid[i][j] = new Hexagon(x+(j*((3*Hexagon.S)/2)), y+((j%2)*Hexagon.A)+(2*i*Hexagon.A));
cp.add(grid[i][j]);
}
}
f.setLayout(null);
f.setBounds(100, 100, 300, 300);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setVisible(true);
}
}
The Hexagon.java class:
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Polygon;
import javax.swing.JButton;
public class Hexagon extends JButton {
public static final int S = 50;
public static final int A = (int) (Math.sqrt(3)*(S/2));
private static final long serialVersionUID = 1L;
private final int x, y;
private final Polygon shape;
public Hexagon(int x, int y) {
this.x = x;
this.y = y;
this.shape = initHexagon();
setSize(2*S, 2*A);
setLocation(x-S, y-A);
setContentAreaFilled(false);
}
private Polygon initHexagon() {
Polygon p = new Polygon();
p.addPoint(x+(S/2), y-A);
p.addPoint(x+S, y);
p.addPoint(x+(S/2), y+A);
p.addPoint(x-(S/2), y+A);
p.addPoint(x-S, y);
p.addPoint(x-(S/2), y-A);
return p;
}
protected void paintComponent(Graphics g) {
g.setColor(Color.BLACK);
g.drawPolygon(this.shape);
}
protected void paintBorder(Graphics g) {
Graphics2D g2 = (Graphics2D) g;
g2.setColor(Color.BLACK);
g2.setStroke(new BasicStroke(4));
g2.drawPolygon(this.shape);
}
public boolean contains(int x, int y) {
return this.shape.contains(x, y);
}
}
As i said, this class worked just fine using non-rectangular shapes.
There was no clipping or such.

You've posted your definition of Hexagon too late, so I copy-pasted a modified version of a similar class from my collection of code snippets.
Here is one way to generate a hexagonal grid:
import java.awt.Container;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JComponent;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Color;
import java.awt.GridLayout;
import java.util.function.*;
public class Hexagons extends JPanel {
private static final long serialVersionUID = 1L;
/** Height of an equilateral triangle with side length = 1 */
private static final double H = Math.sqrt(3) / 2;
static class Hexagon {
final int row;
final int col;
final double sideLength;
public Hexagon(int r, int c, double a) {
this.row = r;
this.col = c;
this.sideLength = a;
}
double getCenterX() {
return 2 * H * sideLength * (col + (row % 2) * 0.5);
}
double getCenterY() {
return 3 * sideLength / 2 * row;
}
void foreachVertex(BiConsumer<Double, Double> f) {
double cx = getCenterX();
double cy = getCenterY();
f.accept(cx + 0, cy + sideLength);
f.accept(cx - H * sideLength, cy + 0.5 * sideLength);
f.accept(cx - H * sideLength, cy - 0.5 * sideLength);
f.accept(cx + 0, cy - sideLength);
f.accept(cx + H * sideLength, cy - 0.5 * sideLength);
f.accept(cx + H * sideLength, cy + 0.5 * sideLength);
}
}
public static void main(String[] args) {
final int width = 50;
final int height = 50;
final Hexagon[][] grid = new Hexagon[height][width];
for(int row = 0; row < height; row++) {
for(int col = 0; col < width; col++) {
grid[row][col] = new Hexagon(row, col, 50);
}
}
JFrame f = new JFrame("Hexagons");
f.getContentPane().setLayout(new GridLayout());
f.getContentPane().add(new JComponent() {
#Override public void paint(Graphics g) {
g.setColor(new Color(0xFF, 0xFF, 0xFF));
g.fillRect(0,0,1000,1000);
g.setColor(new Color(0,0,0));
final int[] xs = new int[6];
final int[] ys = new int[6];
for (Hexagon[] row : grid) {
for (Hexagon h: row) {
final int[] i = {0};
h.foreachVertex((x, y) -> {
xs[i[0]] = (int)((double)x);
ys[i[0]] = (int)((double)y);
i[0]++;
});
g.drawPolygon(xs, ys, 6);
g.drawString(
"(" + h.row + "," + h.col + ")",
(int)(h.getCenterX() - 15),
(int)(h.getCenterY() + 12)
);
}
}
}
});
f.setBounds(0, 0, 500, 500);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setVisible(true);
try {
Thread.sleep(100);
} catch (Throwable e) {
} finally {
f.repaint();
}
}
}
It produces the following output:
Sorry for the lack of anti-aliasing. A few hints:
Height H of an equilateral triangle with unit side length is sqrt(3) / 2
The six offsets from the center are (0, +1), (H, +1/2), (H, -1/2), (0, -1), (-H, -1/2), (-H, +1/2), everything times side length.
Distance between rows is 1.5, distance between columns is 2 * H (times scaling constant = side length).
Every odd row is shifted by (0, H) (times scaling constant).
The position of (row,col)-th hexagon is (1.5 * row, 2 * H * (col + 0.5 * (row % 2))) (times constant).
If you want to rotate the hexagons such that two of their sides are horizontal, you have to flip rows and columns.

Java drawImage() not drawing

Within my program, I have the following code:
package io.github.AdmiralSbs.DiceWars;
import javax.imageio.ImageIO;
import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.*;
import java.util.Scanner;
public class HexDisplay extends JPanel {
private static final long serialVersionUID = 1L;
public static final int SIZE = 200;
private int height;
private int width;
private Hex[][] hex;
private BufferedImage myImage;
private Graphics drawer;
public HexDisplay(File f) throws IOException {
Scanner key = new Scanner(f);
int[] temp = commaSplit(key.nextLine());
height = temp[0];
width = temp[1];
hex = new Hex[width][height];
for (int w = 0; w < width; w++) {
for (int h = 0; h < height; h++) {
//temp = commaSplit(key.nextLine());
if (h % 2 == 0)
hex[w][h] = new Hex((int) (SIZE * (w + 0.5)),
(int) (SIZE * (h + 0.5)), SIZE);
else
hex[w][h] = new Hex((int) (SIZE * (w + 1.5)),
(int) (SIZE * (h + 0.5)), SIZE);
System.out.println(hex[w][h].getX() + " " + hex[w][h].getY());
}
}
key.close();
starting();
ImageIO.write(myImage, "jpg", new File("outPic.jpg"));
}
public void starting() {
setPreferredSize(new Dimension(400,400));
setLayout(new FlowLayout());
myImage = new BufferedImage(400, 400, BufferedImage.TYPE_INT_RGB);
drawer = myImage.getGraphics();
drawer.setColor(Color.BLUE);
drawer.fillRect(0, 0, 400, 400);
drawStuff(drawer);
repaint();
}
public int[] commaSplit(String s) {
String[] str = s.split(",");
int[] ret = new int[str.length];
for (int i = 0; i < str.length; i++) {
ret[i] = Integer.parseInt(str[i]);
}
return ret;
}
public void paintComponents(Graphics g) {
g.drawImage(myImage, 0, 0, this);
System.out.println("Painted");
}
public void drawStuff(Graphics g) {
for (int w = 0; w < width; w++) {
for (int h = 0; h < height; h++) {
hex[w][h].draw(g);
}
}
System.out.println("Drew");
revalidate();
repaint();
paintComponents(g);
}
}
What I would expect to happen is for the frame that contains this JPanel to display the image, but it does not. All System.out.println() methods are called as expected, and I am able to save the image as a .jpg file. However, the image is not displayed in the GUI. What can be done?

You have a typo:
// v
public void paintComponents(Graphics g) {
It should be paintComponent.
And should contain a call to super method:
super.paintComponent(g);
as the first line in the method

Button To Reset The View Of JFrame

I have to write a program that will generate 20 random circles with random radius lengths. If any of these circles intersect with another, the circle must be blue, and if it does not intersect, the color is red. I must also place a button on the JFrame. If this button is pressed, it needs to clear out the JFrame, and generate a new set of 20 circles following the same color rules. I am extremely new to Java Swing and am really stuck. I have everything working except the button. I cannot get a new set of circles to generate. Any help would be greatly appreciated. Thank You.
import java.awt.Graphics;
import javax.swing.JPanel;
import java.util.Random;
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class IntersectingCircles extends JPanel
{
private int[] xAxis = new int [20]; // array to hold x axis points
private int[] yAxis = new int [20]; // array to hold y axis points
private int[] radius = new int [20]; // array to hold radius length
public static void main (String[] args)
{
JFrame frame = new JFrame("Random Circles");
frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add (new IntersectingCircles());
frame.pack();
frame.setVisible(true);
}
public IntersectingCircles()
{
setPreferredSize(new Dimension(1000, 800)); // set window size
Random random = new Random();
// Create coordinates for circles
for (int i = 0; i < 20; i++)
{
xAxis[i] = random.nextInt(700) + 100;
yAxis[i] = random.nextInt(500) + 100;
radius[i] = random.nextInt(75) + 10;
}
}
public void paintComponent(Graphics g)
{
// Add button to run again
JButton btnAgain = new JButton("Run Again");
btnAgain.setBounds(850, 10, 100, 30);
add(btnAgain);
btnAgain.addActionListener(new ButtonClickListener());
// Determine if circles intersect, create circles, color circles
for (int i = 0; i < 20; i++)
{
int color = 0;
for (int h = 0; h < 20; h++)
{
if(i != h)
{
double x1 = 0, x2 = 0, y1 = 0, y2 = 0, d = 0;
x1 = (xAxis[i] + radius[i]);
y1 = (yAxis[i] + radius[i]);
x2 = (xAxis[h] + radius[h]);
y2 = (yAxis[h] + radius[h]);
d = (Math.sqrt(((x2 - x1) * (x2 - x1)) + ((y2 - y1)*(y2 - y1))));
if (d > radius[i] + radius[h] || d < (Math.abs(radius[i] - radius[h])))
{
color = 0;
}
else
{
color = 1;
break;
}
}
}
if (color == 0)
{
g.setColor(Color.RED);
g.drawOval(xAxis[i], yAxis[i], radius[i] * 2, radius[i] * 2);
}
else
{
g.setColor(Color.BLUE);
g.drawOval(xAxis[i], yAxis[i], radius[i] * 2, radius[i] * 2);
}
}
}
private class ButtonClickListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
String action = e.getActionCommand();
if(action.equals("Run Again"))
{
new IntersectingCircles();
}
}
}
}

Suggestions:
Give your class a method that creates the random circles and calls repaint()
This method should create the circles and add them into an ArrayList.
Consider using Ellipse2D to represent your circles, and so you'd have an ArrayList<Ellipse2D>.
Call this method in your class constructor.
Call it again in the button's ActionListener.
Never add button's or change the state of your class from within your paintComponent method. This method is for drawing the circles and drawing them only and nothing more. Your way you will be creating the button each time the paintComponent method is called, so you could be potentially needlessly creating many JButtons
and needlessly slowing down your time-critical painting method.
Instead add the button in the constructor.
Be sure to call super.paintComponent(g) in your paintComponent method as its first call. This will clear the old circles when need be.
Also in paintComponent, iterate through the ArrayList of circles, drawing each one.

After some searching on this website, i found what i needed. Everything seems to work now. Thanks.
import java.awt.Graphics;
import javax.swing.JPanel;
import java.util.Random;
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class IntersectingCircles extends JPanel
{
private int[] xAxis = new int [20]; // array to hold x axis points
private int[] yAxis = new int [20]; // array to hold y axis points
private int[] radius = new int [20]; // array to hold radius length
public static void main (String[] args)
{
JFrame frame = new JFrame("Random Circles");
frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
frame.setPreferredSize(new Dimension(1000, 800));
ActionListener runAgain = new ActionListener()
{
#Override
public void actionPerformed(ActionEvent c)
{
frame.getContentPane().add(new IntersectingCircles());
frame.pack();
}
};
JButton btnAgain = new JButton("Run Again");
btnAgain.setBounds(850, 10, 100, 30);
btnAgain.addActionListener(runAgain);
frame.add(btnAgain);
frame.getContentPane().add (new IntersectingCircles());
frame.pack();
frame.setVisible(true);
}
public IntersectingCircles()
{
Random random = new Random();
// Create coordinates for circles
for (int i = 0; i < 20; i++)
{
xAxis[i] = random.nextInt(700) + 100;
yAxis[i] = random.nextInt(500) + 100;
radius[i] = random.nextInt(75) + 10;
}
}
public void paintComponent(Graphics g)
{
super.paintComponent(g);
// Determine if circles intersect, create circles, color circles
for (int i = 0; i < 20; i++)
{
int color = 0;
for (int h = 0; h < 20; h++)
{
if(i != h)
{
double x1 = 0, x2 = 0, y1 = 0, y2 = 0, d = 0;
x1 = (xAxis[i] + radius[i]);
y1 = (yAxis[i] + radius[i]);
x2 = (xAxis[h] + radius[h]);
y2 = (yAxis[h] + radius[h]);
d = (Math.sqrt(((x2 - x1) * (x2 - x1)) + ((y2 - y1)*(y2 - y1))));
if (d > radius[i] + radius[h] || d < (Math.abs(radius[i] - radius[h])))
{
color = 0;
}
else
{
color = 1;
break;
}
}
}
if (color == 0)
{
g.setColor(Color.RED);
g.drawOval(xAxis[i], yAxis[i], radius[i] * 2, radius[i] * 2);
}
else
{
g.setColor(Color.BLUE);
g.drawOval(xAxis[i], yAxis[i], radius[i] * 2, radius[i] * 2);
}
}
}
}

private class ButtonClickListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
repaint();
}
}
Maybe you can have a try...

JPanel size not changing

Hi guys i'm trying to create a draughts game in Java and am using JPanels to represent the squares, if I were to change the size of the panels how would I do so ? if I use a layout manager the squares are not big enough. At the moment i'm not using a layout manager to try and change the size, but the size doesnt seem to change - just stays at 1,1 pixel.
private void createSquares(){
for(int i = 0; i < 65; i++){
squares[i] = new JPanel();
squares[i].setLayout(null);
squares[i].setSize(20,20);
board.add(squares[i]);
}
}

You could always "borrow" an image or two online, and put that into your program. For example this code:
import java.awt.GridLayout;
import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.URL;
import java.util.*;
import javax.imageio.ImageIO;
import javax.swing.*;
public class GetChessSquareImages {
public static final String PATH_TO_SQUARES = "http://www.colourbox.com/preview/" +
"4578561-622234-seamless-oak-square-chess-like-parquet-texture.jpg";
private static final int IMG_SIDE_COUNT = 4;
private static final double SCALE = 0.8;
private Map<SquareColor, List<Icon>> squareColorMap = new HashMap<SquareColor, List<Icon>>();
private Random random = new Random();
public void downloadImages() throws IOException {
URL lrgImgUrl = new URL(PATH_TO_SQUARES);
BufferedImage largeImg = ImageIO.read(lrgImgUrl);
int w = largeImg.getWidth() / IMG_SIDE_COUNT;
int h = largeImg.getHeight() / IMG_SIDE_COUNT;
for (int i = 0; i < IMG_SIDE_COUNT; i++) {
int x = (i * largeImg.getWidth()) / IMG_SIDE_COUNT;
for (int j = 0; j < IMG_SIDE_COUNT; j++) {
if (j != 1 && j != 2) {
int y = (j * largeImg.getHeight()) / IMG_SIDE_COUNT;
extractSubImg(largeImg, i, j, x, y, w, h);
}
}
}
}
private void extractSubImg(BufferedImage largeImg,
int i, int j, int x, int y, int w, int h) {
Image subImg = largeImg.getSubimage(x, y, w, h);
int width = (int) (w * SCALE);
int height = (int) (h * SCALE);
subImg = subImg.getScaledInstance(width, height, Image.SCALE_SMOOTH);
List<Icon> iconList = null;
if (i % 2 == j % 2) {
iconList = squareColorMap.get(SquareColor.LIGHT);
if (iconList == null) {
iconList = new ArrayList<Icon>();
squareColorMap.put(SquareColor.LIGHT, iconList);
}
} else {
iconList = squareColorMap.get(SquareColor.DARK);
if (iconList == null) {
iconList = new ArrayList<Icon>();
squareColorMap.put(SquareColor.DARK, iconList);
}
}
iconList.add(new ImageIcon(subImg));
}
public Icon getRandomIcon(SquareColor sqrColor) {
List<Icon> iconList = squareColorMap.get(sqrColor);
if (iconList == null) {
return null;
} else {
return iconList.get(random.nextInt(iconList.size()));
}
}
public static void main(String[] args) {
GetChessSquareImages getImages = new GetChessSquareImages();
try {
getImages.downloadImages();
} catch (IOException e) {
e.printStackTrace();
System.exit(-1);
}
int side = 8;;
JPanel panel = new JPanel(new GridLayout(side , side));
for (int i = 0; i < side; i++) {
for (int j = 0; j < side; j++) {
SquareColor sqrColor = (i % 2 == j % 2) ? SquareColor.LIGHT : SquareColor.DARK;
Icon icon = getImages.getRandomIcon(sqrColor);
panel.add(new JLabel(icon));
}
}
JOptionPane.showMessageDialog(null, panel);
}
}
enum SquareColor {
DARK, LIGHT
}
returns this JPanel:
Then your square size will be based on the sizes of your ImageIcons. For example, I have scaled my squares back with a scale factor of 0.8 (the SCALE constant above) to make the grid a more reasonable size.