More bouncing balls...

Hey all!

I need some help with graphics! Here's what I'm trying to do:

I need to create an applet that generates bouncing balls. The number of balls are dependent on buttons used to add and remove them. They all enter the panel from the origin.

Here's what my problem is:

When I click the "+1" button, the ball increases in length and increases in speed -- as if the increment is a multiplier all around. And the "-1" button does the opposite -- however it won't remove the ball at all.

I am utilizing an ArrayList, but really don't understand how to incorporate graphics so I have multiple images -- I just know that this is the data structure I need to use. So, how can I adjust my program to create multiple (unlimited) balls at the click of a button? My code is below.

Thanks!
- SM

Code:

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import java.util.ArrayList;
import java.util.List;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;



public class Exercise18_19 extends JApplet {

  private static List<Ball> ballList = new ArrayList<Ball>(); 
   
  public Exercise18_19() {
    add(new BallControl());
  }

  public static void main(String[] args) {
    Exercise18_19 applet = new Exercise18_19();
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setTitle("BounceBallApp");
    frame.add(applet, BorderLayout.CENTER);
    frame.setSize(400, 320);
    frame.setVisible(true);
  }
   


class BallControl extends JPanel{
  private Ball ball = new Ball();
  private JButton jbtSuspend = new JButton("Suspend");
  private JButton jbtResume = new JButton("Resume");
  private JButton jbtPlusOne = new JButton("+1");
  private JButton jbtMinusOne = new JButton("-1");
  private JScrollBar jsbDelay = new JScrollBar();

  public BallControl() {
    // Group buttons in a panel
    JPanel panel = new JPanel();
    panel.add(jbtSuspend);
    panel.add(jbtResume);
    panel.add(jbtPlusOne);
    panel.add(jbtMinusOne);

    // Add ball and buttons to the panel
    ball.setBorder(new javax.swing.border.LineBorder(Color.red));
    jsbDelay.setOrientation(JScrollBar.HORIZONTAL);
    ball.setDelay(jsbDelay.getMaximum());
    setLayout(new BorderLayout());
    add(jsbDelay, BorderLayout.NORTH);
    add(ball, BorderLayout.CENTER);
    add(panel, BorderLayout.SOUTH);

    // Register listeners
    jbtSuspend.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        ball.suspend();
      }
    });
    jbtResume.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        ball.resume();
      }
    });
    jsbDelay.addAdjustmentListener(new AdjustmentListener() {
      public void adjustmentValueChanged(AdjustmentEvent e) {
        ball.setDelay(jsbDelay.getMaximum() - e.getValue());
      }
    });
    jbtPlusOne.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        ball.increment();
      }
    });
    jbtMinusOne.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        ball.decrement();
      }
    });
  }
}


//***************************************************************



public class Ball extends JPanel {
  private int delay = 1000; 
  // Create a timer with delay 1000 ms
  private Timer timer = new Timer(delay, new TimerListener());

  private int x = 0; private int y = 0; // Current ball position
  private int radius = 5; // Ball radius
  private int dx = 2; // Increment on ball's x-coordinate
  private int dy = 2; // Increment on ball's y-coordinate

  public Ball() {
  timer.start();
  //radius = this.radius;
  //x = this.x;
  //y = this.y;
  //dx = this.dx;
  //dy = this.dy;
  }
 
  @Override
  protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    for (Ball ball : ballList){
          // Check boundaries
      if (x < radius) dx = Math.abs(dx);
      if (x > getWidth() - radius) dx = -Math.abs(dx);
      if (y < radius) dy = Math.abs(dy);
      if (y > getHeight() - radius) dy = -Math.abs(dy);

      // Adjust ball position
      x += dx;
      y += dy;
      g.setColor(Color.red);
      g.fillOval(x - radius, y - radius, radius * 2, radius * 2);
    }//close for loop
  }//close paint method
 
 
  private class TimerListener implements ActionListener {
    /** Handle the action event */
    public void actionPerformed(ActionEvent e) {
      for (Ball ball : ballList){
        repaint();
      }
    }
  }//close timer class

  public void suspend() {
    timer.stop(); // Suspend timer
  }

  public void resume() {
    timer.start(); // Resume timer
  }

  public void setDelay(int delay) {
    this.delay = delay;
    timer.setDelay(delay); //Adjusts delay per slider
  }
 
  public void increment(){
    ballList.add(new Ball());
    System.out.println("plus one");
  }
 
  public void decrement(){
    int last = ballList.size();
    if(last != 0)
    ballList.remove(last-1);
    System.out.println("minus one");
  }
 
 }//close ball class
}//close class -- end of file

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Anyone?

Quote:

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how can I adjust my program to create multiple (unlimited) balls at the click of a button?

---

Use the paintComponent method in the BallControl call to call the balls for them to display themselves. Have a list of balls that it calls passing each the Graphics object.

When you click a button a new button is created and added to the list.

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db

Here is a corrected version with random colors for each ball and avoiding the use of List<> sintaxis that is not yet covered in chapter 18 of Liang´s Java programming book 8th edition from where this exercise is extracted, so unsafe check alert would appear when compiling it.

Code:

---


import java.util.ArrayList;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

public class Exercise18_19 extends JApplet
{
    private static ArrayList ballList = new ArrayList();
    private JButton jbtPlusOne = new JButton("+1");
    private JButton jbtMinusOne = new JButton("-1");

    public Exercise18_19()
    {
        add(new BallControl());
    }

    public static void main(String[] args)
    {
        Exercise18_19 applet = new Exercise18_19();
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setTitle("Exercise18_19");
        frame.add(applet, BorderLayout.CENTER);
        frame.setSize(400, 300);
        frame.setVisible(true);
    }

    class BallControl extends JPanel
    {
        private Ball ball = new Ball();
        private JButton jbtSuspend = new JButton("Suspend");
        private JButton jbtResume = new JButton("Resume");
        private JScrollBar jsbDelay = new JScrollBar();

        public BallControl()
        {
            // Group buttons in a panel
            JPanel panel = new JPanel();
            panel.add(jbtSuspend);
            panel.add(jbtResume);
            panel.add(jbtPlusOne);
            panel.add(jbtMinusOne);

            // Add ball and buttons to the panel
            ball.setBorder(new javax.swing.border.LineBorder(Color.red));
            jsbDelay.setOrientation(JScrollBar.HORIZONTAL);
            ball.setDelay(jsbDelay.getMaximum());
            setLayout(new BorderLayout());
            add(jsbDelay, BorderLayout.NORTH);
            add(ball, BorderLayout.CENTER);
            add(panel, BorderLayout.SOUTH);

            // Register listeners
            jbtSuspend.addActionListener(new ActionListener()
            {
                public void actionPerformed(ActionEvent e)
                {
                    ball.suspend();
                }
            });
            jbtResume.addActionListener(new ActionListener()
            {
                public void actionPerformed(ActionEvent e)
                {
                    ball.resume();
                }
            });
            jsbDelay.addAdjustmentListener(new AdjustmentListener()
            {
                public void adjustmentValueChanged(AdjustmentEvent e)
                {
                    ball.setDelay(jsbDelay.getMaximum() - e.getValue());
                }
            });
            jbtPlusOne.addActionListener(new ActionListener()
            {
                public void actionPerformed(ActionEvent e)
                {
                    ball.increment();
                }
            });
            jbtMinusOne.addActionListener(new ActionListener()
            {
                public void actionPerformed(ActionEvent e)
                {
                    ball.decrement();
                }
            });
        }
    }

    public class Ball extends JPanel
    {
        private int delay = 1000;
        // Create a timer with delay 1000 ms
        private Timer timer = new Timer(delay, new TimerListener());

        private int x = 0;
        private int y = 0; // Current ball position
        private int radius = 5; // Ball radius
        private int dx = 2; // Increment on ball's x-coordinate
        private int dy = 2; // Increment on ball's y-coordinate

        private Color[] colorPalette = new Color[]{Color.red, Color.blue, Color.cyan,
                Color.green, Color.gray, Color.yellow, Color.black, Color.magenta,
                Color.darkGray, Color.LIGHT_GRAY, Color.orange, Color.pink, Color.white};

        private Color color;

        public Ball()
        {
            timer.start();
        }

        public void setColor(Color color)
        {
            this.color = color;
        }

        protected void paintComponent(Graphics g)
        {
            super.paintComponent(g);

            for (Object ball : ballList)  // if you use List<Ball> then change
                                              // to: for(Ball ball : ballList)
            {
                // Check boundaries
                if (((Ball) ball).x < radius) ((Ball) ball).dx = // If you use List<Ball>
                            Math.abs(((Ball) ball).dx);          // instead of ArrayList
                                                                        // change these lines                           
                                                                        // to the following:
                                                                        // if(ball.x < radius)
                                                                        // ball.dx = Math.abs
                                                                        // (ball.dx);
                                                                        // etc., etc...
               
                if (((Ball) ball).x > getWidth() - radius) ((Ball) ball).dx =
                        -Math.abs(((Ball) ball).dx);  // Eliminating Math.abs
                                                              // from this line has
                                                              // the same result
             
                if (((Ball) ball).y < radius) ((Ball) ball).dy =
                        Math.abs(((Ball) ball).dy);
             
                if (((Ball) ball).y > getHeight() - radius) ((Ball) ball).dy =
                        -Math.abs(((Ball) ball).dy);  // Eliminating Math.abs
                                                              // from this line
                                                              // has the same result

                // Adjust ball position
                ((Ball) ball).x += ((Ball) ball).dx;
                ((Ball) ball).y += ((Ball) ball).dy;
                g.setColor(((Ball) ball).color);
                g.fillOval(((Ball) ball).x - radius,
                        ((Ball) ball).y - radius, radius * 2, radius * 2);
            } //close for loop
        } //close paint method


        private class TimerListener implements ActionListener
        {
            /**
            * Handle the action event
            */
            public void actionPerformed(ActionEvent e)
            {
                repaint();
            }
        }//close timer class

        public void suspend()
        {
            timer.stop(); // Suspend timer
            jbtPlusOne.setEnabled(false);
            jbtMinusOne.setEnabled(false);
        }

        public void resume()
        {
            timer.start(); // Resume timer
            jbtPlusOne.setEnabled(true);
            jbtMinusOne.setEnabled(true);
        }

        public void setDelay(int delay)
        {
            this.delay = delay;
            timer.setDelay(delay); //Adjusts delay per slider
        }

        public void increment()
        {
            int colorPaletteIndex = (int) (Math.random() * colorPalette.length);
            Ball tempBall = new Ball();
            tempBall.setColor(colorPalette[colorPaletteIndex]);
            ballList.add(tempBall);
        }

        public void decrement()
        {
            int lastBall = ballList.size();
            if (lastBall >= 1)
                ballList.remove(lastBall - 1);
        }
    } //close ball class
} //close class -- end of file

---

A definitive version:

Code:

---

import java.util.ArrayList;
import java.util.List;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;


public class Exercise18_19 extends JApplet {

    private static List<Ball> ballList = new ArrayList<Ball>();

    public Exercise18_19() {
        add(new BallControl());
    }

    public static void main(String[] args) {
        Exercise18_19 applet = new Exercise18_19();
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setTitle("Exercise18_19");
        frame.add(applet, BorderLayout.CENTER);
        frame.setSize(400, 320);
        frame.setVisible(true);
    }


    class BallControl extends JPanel {
        private Ball ball = new Ball();
        private JButton jbtSuspend = new JButton("Suspend");
        private JButton jbtResume = new JButton("Resume");
        private JButton jbtPlusOne = new JButton("+1");
        private JButton jbtMinusOne = new JButton("-1");
        private JScrollBar jsbDelay = new JScrollBar();

        public BallControl() {
            // Group buttons in a panel
            JPanel panel = new JPanel();
            panel.add(jbtSuspend);
            panel.add(jbtResume);
            panel.add(jbtPlusOne);
            panel.add(jbtMinusOne);

            // Add ball and buttons to the panel
            ball.setBorder(new javax.swing.border.LineBorder(Color.red));
            jsbDelay.setOrientation(JScrollBar.HORIZONTAL);
            ball.setDelay(jsbDelay.getMaximum());
            setLayout(new BorderLayout());
            add(jsbDelay, BorderLayout.NORTH);
            add(ball, BorderLayout.CENTER);
            add(panel, BorderLayout.SOUTH);

            // Register listeners
            jbtSuspend.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    ball.suspend();
                }
            });
            jbtResume.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    ball.resume();
                }
            });
            jsbDelay.addAdjustmentListener(new AdjustmentListener() {
                public void adjustmentValueChanged(AdjustmentEvent e) {
                    ball.setDelay(jsbDelay.getMaximum() - e.getValue());
                }
            });
            jbtPlusOne.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    ball.increment();
                }
            });
            jbtMinusOne.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    ball.decrement();
                }
            });
        }
    }


//***************************************************************


    public class Ball extends JPanel {
        private int delay = 1000;
        // Create a timer with delay 1000 ms
        private Timer timer = new Timer(delay, new TimerListener());

        private int x = 0;
        private int y = 0; // Current ball position
        private int radius = 5; // Ball radius
        private int dx = 2; // Increment on ball's x-coordinate
        private int dy = 2; // Increment on ball's y-coordinate

        private Color[] colorPalette = new Color[]{Color.red, Color.blue, Color.cyan, Color.green, Color.gray, Color.yellow, Color.black, Color.magenta,
                Color.darkGray, Color.LIGHT_GRAY, Color.orange, Color.pink, Color.white};

        private Color color;

        public Ball() {
            timer.start();

        }

        public void setColor(Color color) {
            this.color = color;
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            for (Ball ball : ballList) {
                // Check boundaries
                if (ball.x < radius) ball.dx = Math.abs(ball.dx);
                if (ball.x > getWidth() - radius) ball.dx = -Math.abs(ball.dx);
                if (ball.y < radius) ball.dy = Math.abs(dy);
                if (ball.y > getHeight() - radius) ball.dy = -Math.abs(ball.dy);

                // Adjust ball position
                ball.x += ball.dx;
                ball.y += ball.dy;
                g.setColor(ball.color);
                g.fillOval(ball.x - radius, ball.y - radius, radius * 2, radius * 2);
            }//close for loop
        }//close paint method


        private class TimerListener implements ActionListener {
            /**
            * Handle the action event
            */
            public void actionPerformed(ActionEvent e) {

                repaint();

            }
        }//close timer class

        public void suspend() {
            timer.stop(); // Suspend timer
        }

        public void resume() {
            timer.start(); // Resume timer
        }

        public void setDelay(int delay) {
            this.delay = delay;
            timer.setDelay(delay); //Adjusts delay per slider
        }

        public void increment() {

            int colorPaletteIndex = (int) (Math.random() * colorPalette.length);
            Ball tempBall = new Ball();
            tempBall.setColor(colorPalette[colorPaletteIndex]);
            ballList.add(tempBall);

        }

        public void decrement() {
            int lastBall = ballList.size();
            if (lastBall >= 1)
                ballList.remove(lastBall - 1);
        }
    }//close ball class
}

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