java server

package javaserver;

import java.io.*;
import java.net.*;
import java.awt.*;
import java.awt.event.*;
import java.util.ArrayList;
import javax.swing.*;

public class JavaServer extends JFrame {

    private JTextField userText;
    private JTextArea chatWindow;
    private ServerSocket server;
    private int clientNo = 0;
    private ArrayList<Connection> AllConnections = new ArrayList<Connection>();

    //constructor
    public JavaServer(){
        super("Messenger");
        userText = new JTextField();
        userText.addActionListener(
                new ActionListener(){
                    @Override
                    public void actionPerformed(ActionEvent e) {

                        showMessage("\nSERVER - " + e.getActionCommand());

                        for (int i = 0; i < AllConnections.size(); i++) {
                            try {
                                AllConnections.get(i).output.writeObject("SERVER - " + e.getActionCommand());
                                AllConnections.get(i).output.flush();
                            } catch (IOException ex) {
                                showMessage("\nError occured in sending message");
                            }
                        }
                        userText.setText("");
                    }
                }
        );
        add(userText, BorderLayout.NORTH);
        chatWindow = new JTextArea();
        add(new JScrollPane(chatWindow));
        setSize(300,150);
        setVisible(true);
    }

    public void startRunning(){
        try{
            server = new ServerSocket(6789, 100);
            while(true){
                showMessage("\nWaiting for a connection");
                Socket newConnection = server.accept();
                try{
                    AllConnections.add(new Connection(newConnection));
                    clientNo++;

                }catch(IOException iOException){
                    showMessage("\n Error: A client failed to connect");
                }
            }
        }catch(IOException ioException){
            ioException.printStackTrace();
        }
    }

    private class Connection extends Thread{

        private int ClientID = clientNo;
        private ObjectOutputStream output;
        private ObjectInputStream input;
        private Socket clientSocket;

        //Creates a thread for the client
        Connection(Socket clientThread) throws IOException{
            clientSocket = clientThread;
            output = new ObjectOutputStream(clientThread.getOutputStream());
            output.flush();
            input = new ObjectInputStream(clientThread.getInputStream());
            showMessage("\n Stream are now setup!");


            start();
        }

        //Starts conversation
        @Override
        public void run(){
            String message = "";
            showMessage("\nCLIENT " + ClientID + " - has joined the server");

            do{
                try{
                    message = (String) input.readObject();
                    //Display message to server
                    showMessage("\nCLIENT " + ClientID + " - " + message);

                    //Send message to all clients
                    sendMessage(ClientID, message);

                }catch(ClassNotFoundException classNotFoundException){
                    showMessage("\n idk what that user send!");
                }catch(EOFException ex){
                    //Client properly closed connection
                    break;
                }catch(SocketException ex){
                    //Client prematurely closed connection
                    break;
                }catch (IOException ex) {
                    ex.printStackTrace();
                }
            }while(!message.equals("END"));

            showMessage("\nCLIENT " + ClientID + " - has left the connection");
            //When chat is over. close all connections.
            try {
                output.close();
                input.close();
                clientSocket.close();
                AllConnections.remove(this);
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }
    }

    //updates chatWindow
    private void showMessage(final String text){
        SwingUtilities.invokeLater(
                new Runnable(){
                    public void run(){
                        chatWindow.append(text);
                    }
                }
        );
    }

    //Send message to all clients
    private void sendMessage(int ClientID, final String text){
        for (int i = 0; i < AllConnections.size(); i++) {
            try {
                AllConnections.get(i).output.writeObject(text);
                AllConnections.get(i).output.flush();
            } catch (IOException ex) {
                showMessage("\nError occured in sending message");
            }
        }
    }
}