Networking with multiple clients

Client.java

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Socket;
import java.net.UnknownHostException;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JTextField;

public class Client extends JFrame {
    
    static DataOutputStream out;
    static DataInputStream in;
    static int portNum = 45000;
    
    
    public static void main(String args[]) throws UnknownHostException,
            IOException { 

        Client cGUI = new Client();
        cGUI.setVisible(true);

        Socket cSocket = new Socket("127.0.0.1", portNum);
        out = new DataOutputStream(cSocket.getOutputStream());
        in = new DataInputStream(cSocket.getInputStream());
        
        while(true) {
            @SuppressWarnings("deprecation")
            String fromServer = in.readLine();
            if(fromServer != null)
                System.out.println("FROM SERVER: " + fromServer);
        }
    }

    Client() {
        final JTextField tfInput;
        JButton bSend;
        
        tfInput = new JTextField(40);
        bSend = new JButton("Send to Server");
        bSend.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent event) {
                String input = tfInput.getText().toString();
                try {
                    System.out.println("Sending: " + input);
                    input += '\n';
                    out.writeChars(input);
                } catch (IOException e) {
                    System.out.println("Error sending String");
                }
            }
        });
        setLayout(new FlowLayout());
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        add(tfInput);
        add(bSend);
        pack();
    }
}

MiniServer.java

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

public class MiniServer extends Thread {
    private Socket socket = null;
    static int clientNum;
    static DataInputStream iStream;
    static DataOutputStream oStream;

    public MiniServer(Socket socket) {
        super("MiniServer");
        this.socket = socket;
    }

    public void run() {
        System.out.println("Client " + clientNum + " Connected");
        clientNum++;

        try {
            iStream = new DataInputStream(socket.getInputStream());
            oStream = new DataOutputStream(socket.getOutputStream());
        } catch (IOException e) {
            System.out.println("ERROR: getting InputStream or OutputStream");
        }
        
        String data;
        while(true) {
            //if data has been received from client
            if((data = getInput(iStream)) != null) {
                System.out.println(data);
                data += '\n'; 
                for(int i = 0; i < Server.allClients.length; i++) {
                    try {
                        Server.allClients[i].oStream.writeChars(data);
                    } catch (IOException e) {
                        System.out.println("ERROR: writing to allClients");
                    }
                }
            }
            else {
                System.out.println("No viable data received from client");
                System.out.println("Client may have disconnected. Exiting program.");
                System.exit(-1);
            }
        }
    }

    // helpful methods    
    @SuppressWarnings("deprecation")
    public String getInput(DataInputStream in) {
        String receivedData = "";
        try {
            receivedData = in.readLine();
        } catch (IOException e) {
            System.out.println("ERROR: getting data");
            System.exit(-1);
        }
        return receivedData;
    }
}

Server.java

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;

public class Server {
    
    static MiniServer[] allClients; //contains all connected clients

    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);
        }

        int i = 0;
        allClients = new MiniServer[4];
        
        while(i < 4){
            Socket clientSocket = serverSocket.accept();
            MiniServer mini = new MiniServer(clientSocket);
            allClients[i] = mini;
            mini.start();
    
            System.out.println("Server " + i + " started");
            i++;
        }   
        //serverSocket.close();       
    }
}