RandomMovement

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

public class RandomMovement extends JFrame 
    implements ActionListener {

    int xPos, yPos, direction;
        
    private JPanel panel;
    private Random random;
    private javax.swing.Timer timer;

    public static void main(String[] args) {
        RandomMovement frame = new RandomMovement();
        frame.setSize(700, 700);
        frame.createGUI();
        frame.setVisible(true);
    }

    private void createGUI() {
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        Container window = getContentPane();
        window.setLayout(new FlowLayout() );
        random = new Random();

        panel = new JPanel();
        panel.setPreferredSize(new Dimension(600, 600));
        panel.setBackground(Color.lightGray);
        window.add(panel);
        
        timer = new javax.swing.Timer(200, this);
        timer.start();
        
        xPos = 350;
        yPos = 350;
        direction = 0;
    }

    public void actionPerformed(ActionEvent event) {
        
        Graphics paper = panel.getGraphics();
        paper.setColor(Color.blue);
        paper.fillOval(xPos, yPos, 15, 15);
        direction = random.nextInt(4);
        
        if (direction == 0) {
            paper.setColor(Color.lightGray);
            paper.fillOval(xPos, yPos, 15, 15);
            yPos = yPos - 20;
            yPos = (yPos + 685) % 685;
            paper.setColor(Color.blue);
            paper.fillOval(xPos, yPos, 15, 15);
        }
        
        if (direction == 1) {
            paper.setColor(Color.lightGray);
            paper.fillOval(xPos, yPos, 15, 15);
            yPos = yPos + 20;
            yPos = (yPos + 685) % 685;
            paper.setColor(Color.blue);
            paper.fillOval(xPos, yPos, 15, 15);
        }
        
        if (direction == 2) {
            paper.setColor(Color.lightGray);
            paper.fillOval(xPos, yPos, 15, 15);
            xPos = xPos + 20;
            xPos = (xPos + 685) % 685;
            paper.setColor(Color.blue);
            paper.fillOval(xPos, yPos, 15, 15);
        }
        
        if (direction == 3) {
            paper.setColor(Color.lightGray);
            paper.fillOval(xPos, yPos, 15, 15);
            xPos = xPos - 20;
            xPos = (xPos + 685) % 685;
            paper.setColor(Color.blue);
            paper.fillOval(xPos, yPos, 15, 15);
        }
    }
}