Develop Reference

Java Swing Graphics and Events

I am trying to make a simple game which displays circles on a frame and when clicked the circle should disappear. I am learning how Java Swing works and managed to draw a circle (Wow such an achievement) and figured out how events work. I added an mouseListener to the circle and when clicked for now I want a to get a console log that it has been clicked but the end result is not as expected. No matter where I click I always get the "click" console log. When I try to add a listener to a JButton for example I get the end result. Are events different for graphics?
import javax.swing.*;
import javax.swing.event.MouseInputListener;
import java.awt.*;
import java.awt.event.*;
import java.sql.SQLOutput;
public class CirclePop {
JFrame frame;
Circle circle;
public static void main(String[] args) {
CirclePop circlePop = new CirclePop();
circlePop.drawFrame();
}
public void drawFrame() {
frame = new JFrame();
circle = new Circle();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(circle);
circle.addMouseListener(new Click());
frame.setSize(300, 300);
frame.setVisible(true);
}
class Click implements MouseListener {
#Override
public void mouseClicked(MouseEvent e) {
}
#Override
public void mousePressed(MouseEvent e) {
System.out.println("Pressed");
}
#Override
public void mouseReleased(MouseEvent e) {
}
#Override
public void mouseEntered(MouseEvent e) {
}
#Override
public void mouseExited(MouseEvent e) {
}
}
}
import java.awt.*;
import javax.swing.*;
class Circle extends JPanel {
public void paintComponent(Graphics g) {
g.setColor(Color.red);
g.fillOval(150, 140, 30, 30);
}
}

First of all, you may want to extend MouseAdapter instead of implementing MouseListener. This way you don't have "implement" all these empty methods.
Then, in your mousePressed method you just have to calculate if the click happened inside the circle. This is basically just Pythagoras:
static class ClickListener extends MouseAdapter {
private final Circle circle;
public ClickListener(Circle circle) {
this.circle = circle;
}
#Override
public void mousePressed(MouseEvent e) {
int centerX = circle.getCenterX();
int centerY = circle.getCenterY();
int radius = circle.getRadius();
int clickX = e.getX();
int clickY = e.getY();
// inside circle: (clickX - centerX)^2 + (clickY - centerY)^2 < radius^2
double xSquare = Math.pow(clickX - centerX, 2);
double ySquare = Math.pow(clickY - centerY, 2);
if (xSquare + ySquare < radius * radius) {
System.out.println("pressed");
}
}
}
I've added some fields to Circle class to get access to the properties you need for the calculation:
class Circle extends JPanel {
private final int radius = 30;
private final int centerX = 150;
private final int centerY = 140;
public void paintComponent(Graphics g) {
g.setColor(Color.red);
g.fillOval(centerX, centerY, radius, radius);
}
// getter, etc.
}

You have to implement the MouseListener interface indeed, and after a mouse click, you have to check whether the mouse position is contained in the region of your circle. You could do this manually, by comparing coordinates, but this could be a bit too much work. I think it's easier to rather create a Shape object(Infact this is a good time to learn about it since you're just starting out) that you fill with the respective color, and then just check whether the circle contains the mouse position.
Also, check out the Shape class docs when you've got some spare time.
I've gone ahead and made changes to your code, it now uses an instance of Shape class to create a circle.
Also, instead of implementing the MouseListener interface, I recommend extending MouseAdapter since you're not actually providing any meaningful implementation to any method of the interface except the mousePressed() method.
Lastly, notice the shape.contains(event.getPoint()) in the mousePressed() method, that is what does the trick for checking the coordinates.
The rest of the code should be familiar.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
public class CirclePop {
JFrame frame;
Circle circle;
public static void main(String[] args) {
CirclePop circlePop = new CirclePop();
circlePop.drawFrame();
}
public void drawFrame() {
frame = new JFrame();
circle = new Circle();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(circle);
circle.addMouseListener(new Click());
frame.setSize(300, 300);
frame.setVisible(true);
}
class Click extends MouseAdapter {
#Override
public void mousePressed(MouseEvent e) {
if (circle.shape.contains(e.getPoint())) {
System.out.println("Pressed");
}
}
}
}
class Circle extends JPanel {
Shape shape;
public void paintComponent(Graphics g) {
Graphics2D g2 = (Graphics2D) g;
shape = new Ellipse2D.Double(150, 140, 30, 30);
g2.setColor(Color.red);
g2.fill(shape);
}
}

Okay, so, this isn't going to be short
Let's start with ....
frame = new JFrame();
circle = new Circle();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(circle);
circle.addMouseListener(new Click());
frame.setSize(300, 300);
frame.setVisible(true);
Okay, seems simple enough, but, one thing you've missed is the fact that JFrame, by default, uses a BorderLayout - this means, it will make the child component (and the centre/default position) fill all the available space of the frames viewable space
You can see this if you do something like...
frame = new JFrame();
circle = new Circle();
circle.setBackground(Color.RED);
You will now see that the Circle component occupies the entire frame, so when you click on it, you're clicking the Circle component itself.
This isn't bad, but, you might want to change tact a little. Instead of adding the MouseListener independently of the Circle, have the Circle component make use of its own MouseListener, for example...
class Circle extends JPanel {
public Circle() {
addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
// More to come...
}
});
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.red);
g.fillOval(150, 140, 30, 30);
}
}
This means you get to control much of the logic internally to the class, makes it easier to access some of the more critical information without needing to make a bunch of, potentially, dangerous casts.
So, now we just need to add the logic in to determine if the mouse was clicked within the desirable location or not...
public void mouseClicked(MouseEvent e) {
Point point = e.getPoint();
if (point.x >= 150 && point.x <= 150 + 30 && point.y >= 140 && point.y <= 140 + 30) {
System.out.println("You clicked me :(");
}
}
Okay, that's ... basic
We can simplify it a little and make use of the available functionality within the wider API by making use of the "shapes" API, for example...
class Circle extends JPanel {
private Ellipse2D dot = new Ellipse2D.Double(150, 140, 30, 30);
public Circle() {
addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
Point point = e.getPoint();
if (dot.contains(point)) {
System.out.println("You clicked me :(");
}
}
});
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
g2d.setColor(Color.red);
g2d.fill(dot);
g2d.dispose();
}
}
The benefit of this, apart from contains, is we can change the position of the shape relatively easily and our if statement contains to work 🎉
I do, highly, recommend also having a look at
Performing Custom Painting
Painting in AWT and Swing
2D Graphics Trail
Working with Geometry

java decrease time between mouseMotionListener intervals

I want to create a simple drawing programm in java which currently only draws a line using Graphics.fillOval() and a mouseMotionListener(). The problem is, that if you move the mouse quickly the line gets less precise and the ovals (circles in this case) spread apart.
Here is the code:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Drawing
{
private JFrame window;
private Graphics g;
public Drawing()
{
window=new JFrame();
window.setTitle("Paint_window");
window.setSize(1000,700);
window.setVisible(true);
window.setDefaultCloseOperation(window.EXIT_ON_CLOSE);
g=window.getGraphics();
window.addMouseMotionListener(new MouseMotionAdapter()
{
public void mouseDragged(MouseEvent e)
{
if(SwingUtilities.isLeftMouseButton(e)
{
g.fillOval((int)e.getX(),(int)e.getY(),10,10);
}
}
});
}
}
Is there a way of improving this or a better way to this?

g=window.getGraphics();
First of all you should not be using getGraphics() of a component. Any painting you do will only be temporary and will be erased the first time Swing determines the component needs to be repainted. In you above example just try resizing the frame to see this.
The proper way to do custom painting is to override the paintComponent(...) method of a JPanel and add the panel to the frame. See Custom Painting for more information.
The problem is, that if you move the mouse quickly the line gets less precise and the ovals (circles in this case) spread apart
You will not be able to have an event generated for every pixel the mouse moves.
Instead you need to be able to "draw a line" between consecutive points generated as you drag the mouse.
So you need to store each point in an ArrayList and in the custom painting code iterate through all the points and draw a line.
A basic example to get you started:
import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import javax.swing.JFrame;
import javax.swing.JPanel;
class DrawingPanel extends JPanel
{
private ArrayList<ArrayList<Point>> previous = new ArrayList<ArrayList<Point>>();
private ArrayList<Point> current = new ArrayList<Point>();
private BasicStroke basicStroke;
public DrawingPanel(int strokeSize)
{
basicStroke = new BasicStroke(strokeSize, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND);
MouseAdapter ma = new MouseAdapter()
{
#Override
public void mousePressed(MouseEvent e)
{
current.add( new Point(e.getX(), e.getY()) );
}
#Override
public void mouseDragged(MouseEvent e)
{
current.add( new Point(e.getX(), e.getY()) );
repaint();
}
#Override
public void mouseReleased(MouseEvent e)
{
if (current.size() > 1)
{
previous.add( current );
}
current = new ArrayList<Point>();
}
};
addMouseMotionListener( ma );
addMouseListener( ma );
}
#Override
protected void paintComponent(Graphics g)
{
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setStroke( basicStroke );
// Paint lines from previous drags
for (int i = 0; i < previous.size(); i++)
{
drawLines(g, previous.get(i));
}
// Paint line from current drag
drawLines(g, current);
}
private void drawLines(Graphics g, ArrayList<Point> points)
{
for (int i = 0; i < points.size() - 1; i++)
{
int x = (int) points.get(i).getX();
int y = (int) points.get(i).getY();
int x2 = (int) points.get(i + 1).getX();
int y2 = (int) points.get(i + 1).getY();
g.drawLine(x, y, x2, y2);
}
}
private static void createAndShowGUI()
{
JFrame frame = new JFrame("Drawing Panel");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new DrawingPanel(15));
frame.setSize(400, 400);
frame.setLocationByPlatform( true );
frame.setVisible( true );
}
public static void main(String[] args) throws Exception
{
EventQueue.invokeLater( () -> createAndShowGUI() );
/*
EventQueue.invokeLater(new Runnable()
{
public void run()
{
createAndShowGUI();
}
});
*/
}
}
Using the above approach you will redraw the lines every time the component is repainted.
Another approach is to draw to a BufferedImage and then paint the BufferedImage on the panel. You can check out Custom Painting Approaches for an example of this approach.

How to draw a rectangle moving in a circle around the center of the canvas?

The code is meant to draw a rectangle, which moves in a circle around the center of the canvas one time. The code I currently have is
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.Rectangle2D;
import javax.swing.Timer;
import javax.swing.JComponent;
import javax.swing.JFrame;
public class Q3_Circular extends JComponent {
protected int degree = 0;
protected double xStart;
protected double yStart;
protected Timer timer;
public Q3_Circular() {
timer = new Timer(1000, new TimerCallback()); //creates new times that refreshes every 100 ms, and called the TimerCallback class
timer.start();
}
protected class TimerCallback implements ActionListener {
public void actionPerformed(ActionEvent e) {
if (degree < (2 * Math.PI)){
xStart = getWidth()/2 * Math.cos(degree+1);
yStart = getHeight()/2 * Math.sin(degree+1);
degree+= 1;
repaint();
}
else {
degree += 0;
repaint();
}
}
}
public static void main(String[] args) {
JFrame frame = new JFrame("AnimatedSquare");
Q3_Circular canvas = new Q3_Circular();
frame.add(canvas);
frame.setSize(300, 300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
public void paintComponent(Graphics g){
xStart = (double)(getWidth())/2.0 * Math.cos(degree);
yStart = (double)(getHeight())/2.0 * Math.sin(degree);
Graphics2D g2 = (Graphics2D) g;
g2.draw(new Rectangle2D.Double(xStart,yStart, 25,25));
repaint();
}
}
This code appears to draw the rectangle very quickly around the point (0,0). I'm not sure where the code is wrong.

Your code was confusing. Here's the GUI I created.
When creating a Swing GUI, use the model / view / controller pattern. Create a GUI model, and GUI view, and one or more controllers to modify the model and repaint the view.
Here are the changes I made to your code.
I created a DrawingRectangle class to hold the information about the drawing rectangle. This class is a plain old Java object with getters and setters. This class is the GUI model.
I moved everything out of the main method except for the call to the SwingUtilities invokeLater method. The invokeLater method puts the creation and use of the Swing components on the Event Dispatch thread. Oracle and I insist that all Swing applications start on the Event Dispatch thread.
I create the drawing rectangle in the constructor of the Q3_Circular class. Generally, you create the GUI model, then the GUI view.
I rearranged the JFrame code in the run method to be in the proper order. I removed the setSize method and replaced it with the pack method. We don't care how big the JFrame is. We care how big the drawing panel is.
I created a drawing panel from a JPanel. Here, we set the preferred size of the drawing panel. We extend a JPanel so we can override the paintComponent method.
The paintComponent method does nothing but paint the drawing rectangle. No calculations or anything but painting is done in the paintComponent method. I added a call to the super paintComponent method to maintain the Swing paint chain and clear the drawing panel before I paint the drawing rectangle. I draw the rectangle using the x and y coordinates as the center of the rectangle, rather than the upper left corner. This is the one transformation I do in the drawing code.
I created a drawing animation from a Runnable. You can use a Swing Timer if you want. I find it easier to create my own animation code. This is the GUI controller. Here is where we do the calculations, update the model, and repaint the drawing panel. In the repaint method, I use the SwingUtilities invokeLater method to do the painting on the Event Dispatch thread. I do this because the animation thread is a separate thread.
Here's the code. I put all the classes together so I could paste the code easier. You should separate the classes into different files.
package com.ggl.testing;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.geom.Rectangle2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class Q3_Circular implements Runnable {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Q3_Circular());
}
private static final int DRAWING_WIDTH = 300;
private static final int DRAWING_HEIGHT = DRAWING_WIDTH;
private DrawingRectangle drawingRectangle;
public Q3_Circular() {
int center = DRAWING_WIDTH / 2;
Rectangle2D rectangle = new Rectangle2D.Double(center, center, 32D, 32D);
drawingRectangle = new DrawingRectangle(Color.RED, rectangle);
}
#Override
public void run() {
JFrame frame = new JFrame("Animated Square");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
DrawingPanel drawingPanel = new DrawingPanel(DRAWING_WIDTH,
DRAWING_HEIGHT, drawingRectangle);
frame.add(drawingPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
new Thread(new DrawingAnimation(drawingPanel, drawingRectangle))
.start();
}
public class DrawingPanel extends JPanel {
private static final long serialVersionUID = 8226587438110549806L;
private DrawingRectangle drawingRectangle;
public DrawingPanel(int width, int height,
DrawingRectangle drawingRectangle) {
this.setPreferredSize(new Dimension(width, height));
this.drawingRectangle = drawingRectangle;
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(drawingRectangle.getColor());
Rectangle2D rectangle = drawingRectangle.getRectangle();
int x = (int) Math.round(rectangle.getX());
int y = (int) Math.round(rectangle.getY());
int width = (int) Math.round(rectangle.getWidth());
int height = (int) Math.round(rectangle.getHeight());
g.fillRect(x - width / 2, y - height / 2, width, height);
}
}
public class DrawingAnimation implements Runnable {
private DrawingPanel drawingPanel;
private DrawingRectangle drawingRectangle;
public DrawingAnimation(DrawingPanel drawingPanel,
DrawingRectangle drawingRectangle) {
this.drawingPanel = drawingPanel;
this.drawingRectangle = drawingRectangle;
}
#Override
public void run() {
int xCenter = drawingPanel.getWidth() / 2;
int yCenter = drawingPanel.getHeight() / 2;
double radius = drawingPanel.getWidth() / 3;
for (int degree = 0; degree < 360; degree++) {
double radians = Math.toRadians((double) degree);
double x = radius * Math.cos(radians) + xCenter;
double y = radius * Math.sin(radians) + yCenter;
drawingRectangle.setRectangleOrigin(x, y);
repaint();
sleep(100L);
}
}
private void sleep(long interval) {
try {
Thread.sleep(interval);
} catch (InterruptedException e) {
}
}
private void repaint() {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
drawingPanel.repaint();
}
});
}
}
public class DrawingRectangle {
private final Color color;
private Rectangle2D rectangle;
public DrawingRectangle(Color color, Rectangle2D rectangle) {
this.color = color;
this.rectangle = rectangle;
}
public void setRectangleOrigin(double x, double y) {
rectangle
.setRect(x, y, rectangle.getWidth(), rectangle.getHeight());
}
public Color getColor() {
return color;
}
public Rectangle2D getRectangle() {
return rectangle;
}
}
}

How do I make a sprite move in a custom JPanel?

How do I make a sprite move in a custom JPanel?
I have looked at the similar questions and although one question is similar, it isn't addressing my problem. I have a sprite in a JPanel and I am unable to get it to move. One of the requirements I have to meet for the program is that it must begin moving when a JButton is pressed (Mouse Click). I have the code set-up in a way I believe should work, but it will spit out a long list of errors when I press the button. I'm also required to have the panel be a custom panel class.
What I need to know is this:
Methods (ha) of programming sprite movement.
Continuing to move the sprite without a trail.
Making the sprite bounce off the edges of the panel. Done (Unable to test due to no moving ball)
Here's the code I have (MainClient).
package clientPackage;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
import java.awt.Color;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import logicPack.Logic;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class ClientClass
{
Ball mSolo = new Ball();
private JFrame frame;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
ClientClass window = new ClientClass();
window.frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the application.
*/
public ClientClass()
{
initialize();
}
/**
* Initialize the contents of the frame.
*/
Logic Logical;
Graphics g;
private void initialize() {
frame = new JFrame();
frame.setBounds(100, 100, 590, 520);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().setLayout(null);
SpriteField panel = new SpriteField();
panel.addMouseListener(new MouseAdapter()
{
public void mouseClicked(MouseEvent e)
{
/* int tX = e.getX();
Logical.MoveBallX();
int tY = e.getY();
Logical.MoveBallY();
panel.repaint();*/
Logical.MoveBallX();
Logical.MoveBallY();
panel.repaint();
}
});
panel.setForeground(Color.WHITE);
panel.setBackground(Color.GRAY);
panel.setBounds(64, 92, 434, 355);
frame.getContentPane().add(panel);
JButton btnStart = new JButton("Start");
btnStart.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e)
{
Graphics2D g2 = (Graphics2D)g;
mSolo.DrawSprite(g2 , Logical.MoveBallX(), Logical.MoveBallY());
}
});
btnStart.setBounds(64, 13, 174, 60);
frame.getContentPane().add(btnStart);
}
}
And here are my other Classes (Logic)
package logicPack;
import clientPackage.Ball;
public class Logic
{
Ball mSolo;
public int MoveBallX()
{
int NewX = mSolo.xPos + 50;
return NewX;
}
public int MoveBallY()
{
int NewY = mSolo.yPos + 50;
return NewY;
}
//Motion, force, friction and collision GO HERE ONLY
}
SpriteField
package clientPackage;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JPanel;
public class SpriteField extends JPanel
{
Ball mSolo;
SpriteField()
{
mSolo = new Ball();
repaint();
}
public void paintComponent(Graphics g)
{
super.paintComponent(g);
Graphics2D g2 = (Graphics2D)g;
mSolo.DrawSprite(g2 , mSolo.xPos , mSolo.yPos);
}
}
Ball
package clientPackage;
import java.awt.Color;
import java.awt.Graphics2D;
public class Ball
{
Ball()
{
}
public int xPos = 25;
public int yPos = 25;
int diameter = 25;
public void DrawSprite(Graphics2D g2, int xPos, int yPos)
{
g2.setColor(Color.BLACK);
g2.fillOval(xPos - diameter / 2 , yPos - diameter / 2 , diameter , diameter);
}
}
If you do not understand my Java comments, you can just ignore them.
If you need more details to help me, let me know.
EDIT 1:
Andrew, the closest article I could find used arrow keys to move a sprite. The article was "Sprite not moving in JPanel". All the other articles I found either addressed JPanels without sprites, or animating a sprite. However, I need a JButton that is MouseClicked to simply start the movement, and the ball does not change shape or color. I believe I have the collision part working, but I'm unable to test it until the ball starts moving.
EDIT 2:
LuxxMiner, Thanks for the hints. I have refined my collision portion to be a little more accurate using the getHeight and getWidth methods.
EDIT 3:
MadProgrammer, Thanks...? The problem is not the painting of the ball, I cannot get the ball to move in the first place to repaint it. And the example uses arrow keys, not a mouse click or JButton.

First, take a look at Painting in AWT and Swing and Performing Custom Painting to understand how painting works in Swing.
Let's have a look at the code...
You have a Ball class, which has it's own properties, but then your DrawSprite method passes in values which override these properties?
public class Ball {
Ball() {
}
public int xPos = 25;
public int yPos = 25;
int diameter = 25;
public void DrawSprite(Graphics2D g2, int xPos, int yPos) {
g2.setColor(Color.BLACK);
g2.fillOval(xPos - diameter / 2, yPos - diameter / 2, diameter, diameter);
}
}
What's the point of that? The Ball should paint it's own current state. You should get rid of the additional parameters
public class Ball {
Ball() {
}
public int xPos = 25;
public int yPos = 25;
int diameter = 25;
public void DrawSprite(Graphics2D g2) {
g2.setColor(Color.BLACK);
g2.fillOval(xPos - diameter / 2, yPos - diameter / 2, diameter, diameter);
}
}
ClientClass, Logic and SpriteField all have their own Ball references, none of which is shared so if Logic where to update the state of it's Ball, neither ClientClass or SpriteField would actually see those changes.
In reality, only SpriteField needs an instance of Ball, as it's basically the "ball container", it has the information need to determine if the ball moves out of bounds and wants to know when the ball should be repainted, better to isolate the functionality/responsibility for the Ball to SpriteField at this time.
You also need a means to actually move the ball. While you could use other events, I'd be nice if the ball just moved itself, to this end, you can use a Swing Timer, which won't block the Event Dispatching Thread, but which notifies the registered ActionListener within the context of the EDT, making it safe to update the UI from within.
public class SpriteField extends JPanel {
private Ball mSolo;
private Timer timer;
private int xDelta, yDelta;
public SpriteField() {
mSolo = new Ball();
do {
xDelta = (int) ((Math.random() * 8) - 4);
} while (xDelta == 0);
do {
yDelta = (int) ((Math.random() * 8) - 4);
} while (yDelta == 0);
}
public void start() {
if (timer == null || !timer.isRunning()) {
timer = new Timer(40, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
mSolo.xPos += xDelta;
mSolo.yPos += yDelta;
if (mSolo.xPos - (mSolo.diameter / 2) < 0) {
mSolo.xPos = mSolo.diameter / 2;
xDelta *= -1;
} else if (mSolo.xPos + (mSolo.diameter / 2) > getWidth()) {
mSolo.xPos = getWidth() - (mSolo.diameter / 2);
xDelta *= -1;
}
if (mSolo.yPos - (mSolo.diameter / 2) < 0) {
mSolo.yPos = (mSolo.diameter / 2);
yDelta *= -1;
} else if (mSolo.yPos + (mSolo.diameter / 2) > getHeight()) {
mSolo.yPos = getHeight() - (mSolo.diameter / 2);
yDelta *= -1;
}
repaint();
}
});
timer.start();
}
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
mSolo.DrawSprite(g2);
}
}
Now, all you need to do, is when the "Start" button is clicked, call the start method
public class ClientClass {
private JFrame frame;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
ClientClass window = new ClientClass();
window.frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the application.
*/
public ClientClass() {
initialize();
}
/**
* Initialize the contents of the frame.
*/
// Logic Logical;
private void initialize() {
frame = new JFrame();
frame.setBounds(100, 100, 590, 520);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
SpriteField panel = new SpriteField();
panel.setForeground(Color.WHITE);
panel.setBackground(Color.GRAY);
frame.getContentPane().add(panel);
JButton btnStart = new JButton("Start");
btnStart.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
panel.start();
}
});
frame.getContentPane().add(btnStart, BorderLayout.SOUTH);
}
}

timer.schedule() in not working at all (in Java)

I made a simple program in Java which draws a rectangle on a canvas. And then the rectangle starts moving along X-axis, from left to right.
But the timer.schedule() function is not working. Following is the code:-
package firstanimation;
import java.awt.*;
import java.util.Timer;
public class FirstAnimation {
public static void main(String[] args) {
Frame frame = new Frame("SomeRandomName");
frame.setBounds(50, 50, 700, 500);
frame.setBackground(Color.red);
MyCanvas canvas = new MyCanvas();
frame.add(canvas);
frame.setVisible(true);
Graphics graph = frame.getGraphics();
Timer timer = new Timer();
Task task = new Task(canvas, graph);
timer.schedule(task, 1000,1000);
}
}
package firstanimation;
import java.awt.*;
public class MyCanvas extends Canvas{
public int x,y,width,height;
public MyCanvas()
{
x = 0;
y = 0;
width = 50;
height = 50;
}
#Override
public void paint(Graphics g) {
g.setColor(Color.LIGHT_GRAY);
g.fillRect(x, y, width, height);
}
#Override
public void update(Graphics g) {
x+=10;
g.fillRect(x, y, width, height);
}
}
package firstanimation;
import java.util.TimerTask;
import java.awt.Graphics;
public class Task extends TimerTask{
private MyCanvas canvas;
private Graphics graphics;
public Task(MyCanvas can, Graphics g)
{
super();
canvas = can;
graphics = g;
canvas.paint(g);
}
#Override
public void run() {
canvas.update(graphics);
//throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
}
}
But the strange thing is... Every time i'm maximizing and restoring the frame, the box is moving.
Why is this happening?

"But the strange thing is... Every time i'm maximizing and restoring the frame, the box is moving. Why is this happening?"
Because repaint() is called when you resize which update the graphics, which you should be doing, instead of trying to call paint.
But...
Still many things wrong.
Seeing as this is your first animation (package firstanimation;), let me get you started in the right direction.
Don't use Canvas. Use JPanel or JComponent instead. When you do, don't override paint but paintComponent instead. Also make sure you call super.paintComponent so you aren't let with any paint artifact during the animation.
public class MyCanvas extends JPanel {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
//painting code
}
}
Never use getGraphics on a component to do any painting.
You shouldn't ever have to explicitly call paint. The paint[Component] method will be implicitly called for you. A simple call to repaint() will repaint the component.
I just realized you're using all AWT components. Don't use them, they're out-dated. Instead use Swing component. The majority of them are just prefixed with a J, like Frame -> JFrame. They are in the javax.swing.* package.
For animation use a javax.swing.Timer. You can see more at How to Use Timers. The basic construct is
Timer ( int delayInMillis, ActionListener listener )
where delayInMillis is the time to delay between ticks(in this case animations) and the ActionListener listens for "ticks". Each tick, the actionPerformed of the ActionListener is called. There, you can put the code to update any variables you use for animation.
I suggest you read the tutorials Performing Custom Painting to see the proper way to paint.
Here's a simple example with all the points above mentioned
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
public class AnimateBall extends JPanel {
private static final int D_W = 500;
private static final int D_H = 300;
private Ball ball;
public AnimateBall() {
Random rand = new Random();
int randX = rand.nextInt(D_W);
int randY = rand.nextInt(D_H);
ball = new Ball(randX, randY);
Timer timer = new Timer(15, new ActionListener() {
public void actionPerformed(ActionEvent e) {
ball.animate();
repaint();
}
});
timer.start();
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
ball.drawBall(g);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(D_W, D_H);
}
public class Ball {
int x = 0;
int y = 0; // Current ball position
int dx = 4; // Increment on ball's x-coordinate
int dy = 4; // Increment on ball's y-coordinate
int radius = 15; // Ball radius
public Ball(int x, int y) {
this.x = x;
this.y = y;
}
Color color = new Color((int) (Math.random() * 256),
(int) (Math.random() * 256), (int) (Math.random() * 256));
public void drawBall(Graphics g) {
g.setColor(color);
g.fillOval(x - radius, y - radius, radius * 2, radius * 2);
}
public void animate() {
if (x < 0 || x > getWidth()) {
dx = -dx;
}
if (y < 0 || y > getHeight()) {
dy = -dy;
}
// Adjust ball position
x += dx;
y += dy;
}
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
JFrame frame = new JFrame();
frame.add(new AnimateBall());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
}