Swing JPanel - Drawn graphics duplicate instead of moving

Question

For some reason, my KeyListener works just fine and fires off the Booleans to make down and up true and false and the y value changes according to those Booleans exactly how I want it to. My problem is that for some reason, the red rectangle appears to grow in size rather than move, and I'm pretty sure that it's because the previous frame is not cleared. I tried to use super.paintComponent(g); to clear the frame but this accomplishes nothing. Here's the code:

JFrame:

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

public class H extends JFrame
{
    public H()
    {
        super("Atlas Blade");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setResizable(false);
        pack();

        P p = new P();
        Insets frameInsets = getInsets();

        int frameWidth = p.getWidth()    + 
            (frameInsets.left + frameInsets.right);   
        int frameHeight = p.getHeight()    + (
            frameInsets.top + frameInsets.bottom); 

        setPreferredSize(new Dimension(frameWidth, frameHeight));    
        setLayout(null);   
        add(p);   

        pack();   
        setVisible(true);  
    }
}

JPanel:

import javax.swing.*;
import java.awt.*;
import java.awt.event.KeyListener;
import java.awt.event.KeyEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseEvent;
import java.awt.image.*;

public class P extends JPanel implements KeyListener, Runnable
{

    private long updateCount=0;
    private long paintCount=0;
    private int updatesPerSecond = 50;

    private boolean aLeft,aRight,aDown,aUp=false;
    private boolean up,down,left,right=false;

    int x = 20;
    int y=20;
    Hb box = new Hb(x,y);
    Rectangle rect = new Rectangle(0,300,300,50);
    BufferedImage buffer;


    public P()
    {
        super();
        setSize(600,350);
        //setSize(50,50);
        buffer = new BufferedImage    (600,350,BufferedImage.TYPE_4BYTE_ABGR);
        addKeyListener(this);
        Thread jim = new Thread(this);


    jim.start();


    }
    public void run()
    {
        int waitToUpdate = 1000/updatesPerSecond;
        long startTime = System.nanoTime();

        while(true)
        {
            boolean shouldRepaint = false;
            long currentTime = System.nanoTime();
            long updatesNeeded = (((currentTime-startTime) /     1000000))/ waitToUpdate;

            for(long x = updateCount; x< updatesNeeded; x++)
            {
                updateGame();
                shouldRepaint=true;
                updateCount++;
            }

            if(shouldRepaint)
            {
                paintCount++;
                repaint();
            }
            try
            {
                Thread.sleep(5);
            }
            catch(Exception e)
            {
                e.printStackTrace();
            }
        }
    }
    @Override
    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        Graphics bg = buffer.getGraphics();

        bg.setColor(Color.BLACK);
        bg.drawRect(0,300,300,50);
        bg.setColor(Color.RED);
        bg.fillRect(x,y,35,35);

        g.drawImage(buffer,0,0,null);
    }

    public void updateGame()
    {
        box.updateHitbox(x,y);
        if(down)
        {
            if(!box.center.intersects(rect))
            {
                y++;
                //y=y+40;
            }

        }
        else if(up)
        {
            if(!box.center.intersects(rect))
            {
                y--;
            }
        }

    }

    public void keyPressed(KeyEvent e)
    {
        int code = e.getKeyCode();

        if(code==KeyEvent.VK_A)
        {
            left=true;
            right=false;
            aLeft=true;
            aRight=false;
            aDown=false;
            aUp=false;

        }
        if(code==KeyEvent.VK_D)
        {
            left=false;
            right=true;
            aLeft=false;
            aRight=true;
            aDown=false;
            aUp=false;
        }
        if(code==KeyEvent.VK_S)
        {
            System.out.println(y);

            down=true;
            up=false;
            aLeft=false;
            aRight=false;
            aDown=true;
            aUp=false;
        }
        if(code==KeyEvent.VK_W)
        {
            down=false;
            up=true;
            aLeft=false;
            aRight=false;
            aDown=false;
            aUp=true;
        }

        repaint();
    }
    public void keyTyped(KeyEvent e)
    {

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

        if(code==e.VK_A)
        {
            left=false;
            aLeft=false;
        }
        if(code==e.VK_D)
        {
            right=false;
            aRight=false;
        }
        if(code==e.VK_S)
        {
            down=false;
            aDown=false;
        }
        if(code==e.VK_W)
        {
            up=false;
            aUp=false;
        }
    }

    public void addNotify()
    {
        // call super so the method still does what it was built to do
        super.addNotify();

        // requests focus so that key inputs are sent to this screen
        requestFocus();
    }
}

And the Hb class:

import java.awt.Rectangle;

public class Hb
{
public Rectangle center,left,right,up,down;

public Hb(int x, int y)
{
    center = new Rectangle(x,y,50,50);
    left = new Rectangle(x-1,y+1,1,48);
    right = new Rectangle(x+50,y+1,1,48);
    up = new Rectangle(x+1,y-1,48,1);
    down = new Rectangle(x+1,y+50,48,1);
}

public void updateHitbox(int x, int y)
{
    center = new Rectangle(x,y,50,50);
    left = new Rectangle(x-1,y+1,1,48);
    right = new Rectangle(x+50,y+1,1,48);
    up = new Rectangle(x+1,y-1,48,1);
    down = new Rectangle(x+1,y+50,48,1);
}
}

Answer 1

Your problem is that you're doing all your drawing in the BufferedImage, and that doesn't allow erasure of "dirty" pixels. Instead, only draw in the BufferedImage that which should be a static and unchanging part of the image, usually the background. The foreground image that moves should be painted directly in paintComponent using the Graphcis object given to the method by the JVM.

public P() {
    super();
    setSize(600, 350);  // not recommended
    buffer = new BufferedImage(600, 350, BufferedImage.TYPE_4BYTE_ABGR);
    Graphics bg = buffer.getGraphics();
    bg.setColor(Color.BLACK);
    bg.drawRect(0, 300, 300, 50);
    bg.dispose();

    // ....

}

and

@Override
public void paintComponent(Graphics g) {
    super.paintComponent(g);
    g.drawImage(buffer, 0, 0, null);
    g.setColor(Color.RED);
    g.fillRect(x, y, 35, 35);
}