Ball.java

package lesson9;

import java.awt.*;

public class Ball implements Runnable{

    private int x;
    private int y;
    private int speed;
    private Color color;

    public Ball() {
    }

    public Ball(int x, int y, int speed, Color color) {
        this.x = x;
        this.y = y;
        this.speed = speed;
        this.color = color;
    }

    public int getX() {
        return x;
    }

    public void setX(int x) {
        this.x = x;
    }

    public int getY() {
        return y;
    }

    public void setY(int y) {
        this.y = y;
    }

    public int getSpeed() {
        return speed;
    }

    public void setSpeed(int speed) {
        this.speed = speed;
    }

    public Color getColor() {
        return color;
    }

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

    public void draw(Graphics g) {

        g.setColor(this.color);
        g.fillOval(x, y, 40, 40);
    }

    @Override
    public void run() {

        while (true) {
            for (int i = 0; i < 536; i ++) {
                x += 1;
                try {
                    Thread.sleep(speed);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                if (x < 536) {
                    continue;
                }
                break;
            }
            for (int i = 0; i < 536; i ++) {
                x -= 1;
                try {
                    Thread.sleep(speed);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

DemoBalls.java

package lesson9;


public class DemoBalls {

    public static void main(String[] args) {

        ViewPanel panel = new ViewPanel();
        panel.runBalls();
    }
}

ViewPanel.java

package lesson9;

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

public class ViewPanel extends JPanel{

    final int BF_WIDTH = 576;
    final int BF_HEIGHT = 576;
    private List<Ball> ballList;

    public ViewPanel() {

        ballList = new ArrayList<>();
        JFrame frame = new JFrame("Flying ball");
        frame.setLocation(500, 150);
        frame.setMinimumSize(new Dimension(BF_WIDTH, BF_HEIGHT + 22));
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.getContentPane().add(this);
        setBallList();
        frame.pack();
        frame.setVisible(true);
    }

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

        for (Ball b : ballList) {
            b.draw(g);
        }
    }

    public void setBallList() {

        ballList.add(new Ball(0, 0, 2, Color.YELLOW));
        ballList.add(new Ball(0, 50, 3, Color.MAGENTA));
        ballList.add(new Ball(0, 100, 1, Color.GREEN));
        ballList.add(new Ball(0, 150, 5, Color.BLUE));
        ballList.add(new Ball(0, 200, 4, Color.PINK));
        ballList.add(new Ball(0, 250, 8, Color.DARK_GRAY));
        ballList.add(new Ball(0, 300, 6, Color.RED));
        ballList.add(new Ball(0, 350, 9, Color.CYAN));
        ballList.add(new Ball(0, 400, 10, Color.ORANGE));
    }

    public void runBalls() {

        for (Ball b : ballList) {
            new Thread(b).start();
            try {
                Thread.sleep(25);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        while (true) {
            repaint();
            try {
                Thread.sleep(16);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}