LineArt.java

// LineArt.java

import java.awt.*;
import javax.swing.*;

class LineArt {
    public static void main(String[] args) {
    JFrame frame = new JFrame();

    frame.setTitle("Line Art");
    frame.setSize(640, 480);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    MyPanel panel = new MyPanel();
    frame.getContentPane().add(panel);

    frame.setVisible(true);
    }
}

class MyPanel extends JPanel implements Runnable {
    private Ball ball1;
    private Ball ball2;

    public MyPanel() {
    setBackground(Color.white);

    ball1 = new Ball(100,100,10,5,0,0,630,450);
    ball2 = new Ball(200,100,5,10,0,0,630,450);

    Thread refresh = new Thread(this);
    refresh.start();
    }

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

    ball1.forward();
    ball2.forward();

    g.setColor(Color.red);
    g.drawLine(ball1.getX(), ball1.getY(), ball2.getX(), ball2.getY());

    //g.fillOval(ball1.getX(), ball1.getY(), 10, 10 );

    //g.setColor(Color.blue);
    //g.fillOval(ball2.getX(), ball2.getY(), 10, 10 );
    }

    public void run() {
    while(true) {
        repaint();
        try {
        Thread.sleep(20);
        //Thread.sleep(50);
        }
        catch(Exception e) {
        }
    }
    }
}

class Ball {
    private int x;
    private int y;
    private int vx;
    private int vy;
    private int left;
    private int right;
    private int top;
    private int bottom;

    public Ball(int x, int y, int vx, int vy, int l, int t, int r, int b) {
    this.x = x;
    this.y = y;
    this.vx = vx;
    this.vy = vy;
    right = r;
    left = l;
    top = t;
    bottom = b;
    }

    public void forward() {
    x = x + vx;
    y = y + vy;

    if (x < left || x > right) {
        vx = -vx;
    }
    if (y < top || y > bottom) {
        vy = -vy;
    }
    }

    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;
    }
}