Problem with sprite

[romulo]

I’m trying to create an enemy every 10 seconds and make it appear on the screen with different moves.
The problem is that the enemy does not appear on the screen.
I tried to create an array list and add and then draw. But I do not know if I’m doing it right.
Here is the class which controls the game:

package projeto1;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.image.BufferedImage;
import java.util.ArrayList;

import javax.swing.JPanel;

public class PainelJogo extends JPanel implements Runnable {

    public static int TELA_LARGURA = 640;
    public static int TELA_ALTURA = 480;
    private Jogador jogador;    
    private ArrayList<Inimigo> inimigo = new ArrayList();
    long tempoAnterior = System.currentTimeMillis();
    float timer;
    int cont = 0;
    private BufferedImage buffer;
    private Graphics grafico;
    private double difTempo = 0; 
    
    public PainelJogo() {
        setPreferredSize(new Dimension(TELA_LARGURA, TELA_ALTURA));
        setFocusable(true);
        requestFocus();

        buffer = new BufferedImage(TELA_LARGURA, TELA_ALTURA,
                BufferedImage.TYPE_4BYTE_ABGR);
        grafico = buffer.getGraphics(); 
        
        jogador = new Jogador();// Create player
        
        //Set initial position to player
        jogador.setX(100);
        jogador.setY(200);
        
        
        

        addKeyListener(new KeyListener() {

            public void keyTyped(KeyEvent e) {}

            public void keyPressed(KeyEvent e) {
                if (e.getKeyCode() == KeyEvent.VK_LEFT)
                    jogador.setLeft(true);
                if (e.getKeyCode() == KeyEvent.VK_RIGHT)
                    jogador.setRight(true);
                if (e.getKeyCode() == KeyEvent.VK_UP)
                    jogador.setUp(true);
                if (e.getKeyCode() == KeyEvent.VK_DOWN)
                    jogador.setDown(true);
            }

            public void keyReleased(KeyEvent e) {
                if (e.getKeyCode() == KeyEvent.VK_LEFT)
                    jogador.setLeft(false);
                if (e.getKeyCode() == KeyEvent.VK_RIGHT)
                    jogador.setRight(false);
                if (e.getKeyCode() == KeyEvent.VK_UP)
                    jogador.setUp(false);
                if (e.getKeyCode() == KeyEvent.VK_DOWN)
                    jogador.setDown(false);
            }
        });

        Thread t = new Thread(this);          
        t.start();                


    }

    public void paint(Graphics g) {
        super.paint(g);
        g.drawImage(buffer, 0, 0, null);
    }
    
    public void run() {
         
        while(true) {
           
            difTempo = ((double) (System.currentTimeMillis() - tempoAnterior)) / 1000f;    
            tempoAnterior = System.currentTimeMillis();
            timer += difTempo;
            
            if(timer > 10000)
            {
                inimigo.add(new Inimigo());
                inimigo.get(cont).desenha(grafico);                            
                inimigo.get(cont).atualiza(difTempo);            
            }
            
            grafico.setColor(Color.WHITE);
            grafico.fillRect(0, 0, TELA_LARGURA, TELA_ALTURA);
            jogador.atualiza(0);
            jogador.desenha(grafico);
            
            cont++;
            this.paintImmediately(0, 0, TELA_LARGURA, TELA_ALTURA);
        }                    
        }                          
    }