ButtonListener.java

public class buttonListener implements ActionListener {
    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == okButton) {
          
            // only close window if user has entered a name
            if (getInput().compareTo("") != 0) {
                
                if(MiniServer.isNameTaken(getInput()))
                    System.out.println("isNameTaken RESULT = TRUE");
                
                
                // Send name to server
                try {
                    Siege.sendToServer("NAME: " + getInput());
                    System.out.println("Name sending to server...");
                } catch (IOException e1) {
                    System.out.println("ERROR: SENDING NAME TO SERVER");
                }
                setVisible(false);
            }
        }
    }
}

MiniServer.java

package com.eecs285.siegegame;

import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.Socket;

public class MiniServer extends Thread {
    private Socket socket = null;
    String playerName;
    int clientNum;
    BufferedReader iStream;
    DataOutputStream oStream;

    public MiniServer(Socket socket, int numClient) {
        super("MiniServer");
        clientNum = numClient;
        this.socket = socket;
    }

    public void run() {
        // Announce connection of player
        System.out.println("Player " + clientNum + " Connected");

        // get IO functionality to client
        try {
            DataInputStream is = new DataInputStream(socket.getInputStream());
            iStream = new BufferedReader(new InputStreamReader(is));
            oStream = new DataOutputStream(socket.getOutputStream());
        } catch (IOException e) {
            System.out.println("ERROR: getting InputStream or OutputStream");
        }

        // first, get name from user
        
        // Sorry that this part of the code is so confusing/ugly. 
        // In short, all it does is determine whether the string sent to
        // the server contains "NAME", as that is how I specified that a name
        // is being sent to the server
        
        String data;
        boolean namePicked = false;
        while (!namePicked) {
            if ((data = getInput(iStream)) != null) {
                String usableData = "";
                for (int i = 0; i < data.length(); i++) {
                    if (Character.isLetterOrDigit(data.charAt(i)))
                        usableData += data.charAt(i);
                }

                if (usableData.contains("NAME")) {
                    usableData = usableData.substring(4);
                    Server.playerNames[clientNum] = usableData;

                    if (isNameTaken(usableData))
                        System.out.println("Name taken result = true");

                    playerName = usableData;
                    System.out.println("Player " + clientNum
                            + " has changed their name to " + usableData);
                    broadcastToClients("Player " + clientNum
                            + " has changed their name to " + usableData + '\n');
                    namePicked = true;
                }
            }
        }

        while (true) {
            // if data has been received from client
            if ((data = getInput(iStream)) != null) {
                System.out.println(data);
                data += '\n';
                broadcastToClients(data);
            }
        }
    }

    // helpful methods
    public String getInput(BufferedReader istream) {
        String receivedData = null;
        try {
            receivedData = istream.readLine();
        } catch (IOException e) {
            System.out.println("ERROR: getting data");
            System.exit(-1);
        }
        return receivedData;
    }

    public void broadcastToClients(String data) {
        for (int i = 0; i < Server.allClients.length; i++) {
            if (Server.allClients[i] == null)
                continue;
            try {
                Server.allClients[i].oStream.writeChars(data);
            } catch (Exception e) {
                System.out.println("ERROR: writing to server: " + i);
            }
        }
    }
    
    
    // Server.playerNames[] should contain the input string only 
    // once if the name hasn't been picked before
    public static boolean isNameTaken(String input) {
        int numOccurences = 0;
        System.out.println("in isNameTaken");
        System.out.println(" input = " + input);
        for (int i = 0; i < Server.MAX_PLAYERS; i++) {
            System.out.println("   i = " + i);
            System.out.println("   playerNames[i] = " + Server.playerNames[i]);
            if (Server.playerNames[i].contentEquals(input)) {
                numOccurences++;
            }
        }
        if (numOccurences > 1) // this instance of the name will be in the array
            return true;

        return false;
    }
}

Server.java

package com.eecs285.siegegame;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;


public class Server {
    
    static MiniServer[] allClients; //contains all connected clients
    static String[] playerNames = {"Player 0", "Player 1", "Player 2", "Player 3"}; //contains all player names
    static boolean connectionAllowed = true; //if additional players can join
    static int numPlayer = 0;
    final static int MAX_PLAYERS = 4;

    public static void main(String[] args) throws IOException {        
        
        ServerSocket serverSocket = null;        
        try {
            serverSocket = new ServerSocket(45000);
        } catch (IOException e) {
            System.err.println("Could not listen on port: 45000");
            System.exit(-1);
        }

        allClients = new MiniServer[MAX_PLAYERS];    
        
        while(connectionAllowed && numPlayer < MAX_PLAYERS) {         
            //accept connection and start a new MiniServer for that client
            Socket clientSocket = serverSocket.accept();
            MiniServer server = new MiniServer(clientSocket, numPlayer);
            allClients[numPlayer] = server;
            server.start();
    
            System.out.println("Server " + numPlayer + " started"); 
            numPlayer++;
        }       
    }
}