java.net.ConnectException: Connection refused: connect

import java.io.DataInputStream;
import java.io.InputStream;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;
 
 
public class Cliente {
	//Constantes
	final int PUERTO = 7000;
	//final String HOST = "192.168.1.36";
 
	/************/
 
	//Métodos - constructor
	public Cliente(){
 
		try{
			InetAddress address = InetAddress.getLocalHost();
			Socket skCliente;
 
			skCliente = new Socket(address, PUERTO);
			InputStream aux = skCliente.getInputStream();
			DataInputStream flujo = new DataInputStream(aux);
			System.out.println(flujo.readUTF());
			skCliente.close();
 
		} catch(UnknownHostException e){
			System.out.println( e );
		    System.out.println("Error en la conexión." );
 
		} catch (Exception e) {
			System.out.println(e);
 
		}
	}
 
	//Cuerpo del programa
	public static void main(String[] args){
		new Cliente();
 
 
	}
 
}
 

import java.io.DataOutputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;
 
 
public class Servidor {
	//Constantes
	final int MAX_CLIENTES = 5;
	final int PUERTO = 7000;
	/************/
 
	//Métodos - constructor
	public Servidor(){
		ServerSocket skServidor;
		try {
			skServidor = new ServerSocket(PUERTO);
			System.out.println("Escucho el puerto: "+PUERTO);
			for(int numCli = 0; numCli < MAX_CLIENTES; numCli++){
				Socket skCliente = skServidor.accept();
				System.out.println("\tSirvo al cliente: "+skCliente.getRemoteSocketAddress());
				OutputStream aux = skCliente.getOutputStream();
				DataOutputStream flujo = new DataOutputStream(aux);
				flujo.writeUTF("\nHola cliente "+ skCliente.getRemoteSocketAddress());
				skCliente.close();
			}
 
		} catch(UnknownHostException e){
			System.out.println( e );
		    System.out.println("Error en la conexión." );
 
		}
		    catch (Exception e) {
			// TODO Auto-generated catch block
			System.out.println(e);
		}
	}
 
	public static void main(String[] args){
		new Servidor();
	}
}
 

Exception in thread "main" java.lang.IllegalArgumentException: input == null!
	at javax.imageio.ImageIO.read(ImageIO.java:1348)
	at ImageJPanel$PanelOverDraw.<init>(ImageJPanel.java:40)
	at ImageJPanel.<init>(ImageJPanel.java:25)
	at ImageJPanel.main(ImageJPanel.java:19)

this.add(new PanelOverDraw());

import java.awt.Color;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.Graphics;
 
import javax.swing.ImageIcon;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
 
public class Demo1 extends JComponent {
 
 
    private final static int ANCHO = 512;
 
    private final static int ALTO = 384;
 
    private final static int DIAMETRO = 20;
 
    private float x, y;
 
    private float vx, vy;
 
    public Demo1() {
        setPreferredSize(new Dimension(ANCHO, ALTO));
        x = 10;
        y = 20;
        vx = 300;
        vy = 400;
    }
 
    private void fisica(float dt) {
        x += vx * dt;
        y += vy * dt;
        if (vx < 0 && x <= 0 || vx > 0 && x + DIAMETRO >= ANCHO)
            vx = -vx;
        if (vy < 0 && y < 0 || vy > 0 && y + DIAMETRO >= ALTO)
            vy = -vy;
    }
 
    public void paint(Graphics g) {
 
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, ANCHO, ALTO);
        g.setColor(Color.RED);
        g.fillOval(Math.round(x), Math.round(y), DIAMETRO, DIAMETRO);
    }
 
    private void dibuja() throws Exception {
    	this.repaint();
    }
 
    public void cicloPrincipalJuego() throws Exception {
        float dt = 0.01f;
        while (true) {
        	Thread.sleep(10);
        	fisica(dt);
            dibuja();
        }
    }
 
    public static void main(String[] args) throws Exception {
    	JFrame jf = new JFrame("Demo1");
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jf.setResizable(false);
 
        Demo1 demo1 = new Demo1();
        jf.setContentPane(crearPanel());
        jf.pack();
        jf.setVisible(true);
        demo1.cicloPrincipalJuego();
    }
 
	private static Container crearPanel() {
		JPanel panel = new JPanel();
		JLabel label = new JLabel();
 
		label.setIcon(new ImageIcon("img.jpg"));
		panel.add(label);
 
		return panel;
	}
}