Tile Example

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.Random;
import static java.awt.event.KeyEvent.*;

public class Tiles extends JPanel implements KeyListener {
    static final int tilesPerRow = 8, tilesPerColumn = 6;
    static final int ballDiameter = 20;
    static final Color ballColor = Color.BLACK;
    static Random rand = new Random();
    double speedX = 0, speedY = 0;
    double posX = 20, posY = 20; // position of the ball
    Color[][] tileMap;
    int tileWidth, tileHeight, tileMapWidth, tileMapHeight;

    public static void main(String[] args) throws Exception {
        JFrame frame = new JFrame();
        Tiles panel = new Tiles();
        panel.setPreferredSize(new Dimension(800, 600));
        frame.addKeyListener(panel);
        frame.add(panel);
        frame.pack();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
        panel.run();
    }

    public Tiles() {
        tileMap = new Color[20][20];
        for(int y = 0; y < tileMap.length; y++) {
            for(int x = 0; x < tileMap[0].length; x++) {
                tileMap[y][x] = new Color(rand.nextInt(0xFFFFFF));
            }
        }
    }

    public void run() throws Exception {
        tileWidth = getWidth()/tilesPerRow;
        tileHeight = getHeight()/tilesPerColumn;
        tileMapWidth = tileMap[0].length*tileWidth;
        tileMapHeight = tileMap.length*tileHeight;
        while(true) {
            posX += speedX; posY += speedY;
            if(posX < 0) posX = 0;
            if(posY < 0) posY = 0;
            if(posX > tileMapWidth) posX = tileMapWidth;
            if(posY > tileMapHeight) posY = tileMapHeight;
            Thread.sleep(16);
            repaint();
        }
    }

    public void keyPressed(KeyEvent e) {
        switch(e.getKeyCode()) {
            case VK_LEFT: speedX = -5; break;
            case VK_RIGHT: speedX = 5; break;
            case VK_UP: speedY = -5; break;
            case VK_DOWN: speedY = 5; break;
        }
    }
    public void keyReleased(KeyEvent e) {
        switch(e.getKeyCode()) {
            case VK_LEFT: if(speedX < 0) speedX = 0; break;
            case VK_RIGHT: if(speedX > 0) speedX = 0; break;
            case VK_UP: if(speedY < 0) speedY = 0; break;
            case VK_DOWN: if(speedY > 0) speedY = 0; break;
        }
    }
    public void keyTyped(KeyEvent e) {
    }
    public void paint(Graphics g) {

        //calculate coordinates of the upper left corner of the tileMap
        int originX = getWidth()/2-(int)posX;
        int originY = getHeight()/2-(int)posY;
        if(originX > 0) originX = 0;
        if(originY > 0) originY = 0;
        //calculate the lower right corner of the tileMap
        int lrX = originX + tileMapWidth;
        int lrY = originY + tileMapHeight;
        if(lrX < getWidth()) {
            originX = getWidth()-tileMapWidth;
            lrX = getWidth();
        }
        if(lrY < getHeight()) {
            originY = getHeight()-tileMapHeight;
            lrY = getHeight();
        }

        //draw the tiles
        for(int y = 0; y < tileMap.length; y++) {
            for(int x = 0; x < tileMap[0].length; x++) {
                int tx = x*tileWidth + originX;
                int ty = y*tileHeight + originY;
                if(tx + tileWidth >= 0 && ty + tileHeight >= 0 && tx < getWidth() && ty < getHeight()) {
                    g.setColor(tileMap[y][x]);
                    g.fillRect(tx, ty, tileWidth, tileHeight);
                }
            }
        }
        g.setColor(ballColor);
        g.fillOval(originX+(int)posX-ballDiameter/2, originY+(int)posY-ballDiameter/2, ballDiameter, ballDiameter);
    }
}