如何让对象独立移动？ （JAVA）

Question

一个物体应该如何自行移动？我的下面的项目是一个简单的Ping Pong游戏翻拍的当前代码。我已成功通过用户输入使左侧Paddle移动，但我不知道如何编程Ball对象和AI Paddle对象独立移动。我怀疑我需要多个线程，但是我在哪里放置它们以及如何从线程内更新我的对象？

也许我把Ball和Paddle对象错放到错误的班级？

主要类别：

package com.N00744323.pingpong;

import javax.swing.JFrame;

public class Display 
{   
    static JFrame frame;
    public static void main(String[] args) 
    {
        frame = new JFrame("Ping Pong");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        frame.getContentPane().add(new GUI());

        frame.pack();
        frame.setVisible(true);
    }
}

GUI框架类：

package com.N00744323.pingpong;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.JPanel;

public class GUI extends JPanel
{
    private static final long serialVersionUID = 1L;

    final private int WIDTH = 750, HEIGHT = 500;

    private Paddle p1, p2;
    private Ball b;

    public GUI()
    {   
        addKeyListener(new DirectionListener());
        p1 = new Paddle(1);
        p2 = new Paddle(2);
        b = new Ball();
        setBackground(Color.black);

        setPreferredSize(new Dimension(WIDTH, HEIGHT));
        setFocusable(true);
    }

    public int getWIDTH()
    {
        return WIDTH;
    }
    public int getHEIGHT()
    {
        return HEIGHT;
    }

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

        page.setColor(Color.black);
        page.fillRect(0, 0, WIDTH, HEIGHT);

        page.setColor(Color.white);
        page.fillRect(p1.getLocX(), p1.getLocY(), p1.getWIDTH(), p1.getHEIGHT());
        page.fillRect(p2.getLocX(), p2.getLocY(), p2.getWIDTH(), p2.getHEIGHT());

        page.fillOval(b.getLoc()[0], b.getLoc()[1], b.getSIZE()*2, b.getSIZE()*2);
    }

    private class DirectionListener implements KeyListener
    {
        public void keyPressed(KeyEvent e) 
        {
            int key = e.getKeyCode();
            if(key == (KeyEvent.VK_UP))
            {
                p1.setLocY(-3);
                System.out.println("Up!");
            }
            else    
                if(key == (KeyEvent.VK_DOWN))
                {
                    p1.setLocY(3);
                    System.out.println("Down!");
                }
            repaint();
        }

        public void keyReleased(KeyEvent e) 
        {
            int key = e.getKeyCode();

            if(key == (KeyEvent.VK_UP))
            {
                System.out.println("Up stopped!");
            }
            else    
                if(key == (KeyEvent.VK_DOWN))
                {
                    System.out.println("Down stopped!");
                }
        }

        public void keyTyped(KeyEvent e) 
        {
            int key = e.getKeyCode();

            if(key == (KeyEvent.VK_UP))
            {
                p1.setLocY(-2);
                System.out.println("Up!");
            }
            else    
                if(key == (KeyEvent.VK_DOWN))
                {
                    p1.setLocY(2);
                    System.out.println("Down!");
                }

            repaint();
        }
    }
}

Paddle对象类：

package com.N00744323.pingpong;

public class Paddle
{
    final private int WIDTH = 10, HEIGHT = 45;
    private int locY, locX;

    public Paddle(int player)
    {
        if(player == 1)
        {
            locY = (500/2) - HEIGHT;
            locX = 20;
        }
        if(player == 2)
        {
            locY = (500/2) - HEIGHT;
            locX = 750-WIDTH-20;
        }
    }

    public void setLocY(int locY)
    {
        if(locY + this.locY >= 0 && this.locY + locY <= 500 - HEIGHT)
            this.locY += locY;
    }

    public int getLocY()
    {
        return locY;
    }

    public int getLocX()
    {
        return locX;
    }

    public int getWIDTH()
    {
        return WIDTH;
    }

    public int getHEIGHT()
    {
        return HEIGHT;
    }
}

球对象类：

package com.N00744323.pingpong;

public class Ball
{
    final private int SIZE = 5;
    private int x, y;

    public Ball()
    {
        x = (750/2) - SIZE*2;
        y = (500/2) - SIZE*2;
    }

    public int getSIZE()
    {
        return SIZE;
    }

    public int[] getLoc()
    {
        int[] pos = {x, y};
        return pos;
    }

    public void setLoc(int[] pos)
    {
        x = pos[0];
        y = pos[1];
    }
}

谢谢！