How do I move an object using Keyboard Control?

Question

Alright, so I created some very basic code. I know how I can make an object move, but I want to know how I can make the object move with the keyboard. For example, W for forward, A for left, S for backward, and D for right.

Here's the code:

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;

import javax.swing.JFrame;
import javax.swing.JPanel;

@SuppressWarnings("serial")
public class Game extends JPanel {

    int x = 0;
    int y = 0;

    /*private void moveBall() {  // This patch is where the movement was before
        x = x + 1;
        y = y + 1;
    } */
    @Override
    public void paint(Graphics g) {
        super.paint(g);
        Graphics2D g2d = (Graphics2D) g;
        g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g2d.fillOval(x, y, 30, 30); // This is the object to move w/ keyboard
    }

    public static void main(String [] args) throws InterruptedException {
        JFrame frame = new JFrame("Frame");
        Game game = new Game();
        frame.add(game);
        frame.setSize(500, 420);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        while(true) {
            game.repaint();
            Thread.sleep(10);
        }
    }
}