Java

import java.io.*; 
import java.net.*; 

class TCPServer { 

	private String  capitalizedSentence; 
	private ServerSocket welcomeSocket;
	private String clientSentence = new String(" d");
	private BufferedReader inFromClient;
	private DataOutputStream  outToClient;
	private Socket connectionSocket;
	  
	private static TCPServer instance = null;
	  
	 private TCPServer() throws Exception {
	  
	  }
	  
	private  TCPServer(int socketID) throws Exception {
	  if( welcomeSocket==null){
	 
		 }
	}
	
	
	
	public static TCPServer getInstance() throws Exception {
      if(instance == null) {
         instance = new TCPServer();
		 System.out.println("This is new server instance created");
      }
	  else if(instance !=null){
	  System.out.println("This is old instance");
	  }
	  
      return instance;
   }
	
	public void method()
	{
		System.out.println("This is server");
	}
	public void run() throws Exception{
	 welcomeSocket = new ServerSocket(6789); 
		 while(clientSentence.equals("exit")!=true) { 
		  connectionSocket = welcomeSocket.accept(); 
		  inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream())); 
          outToClient = new DataOutputStream(connectionSocket.getOutputStream()); 
           clientSentence = inFromClient.readLine(); 
           System.out.println("Recived from client : " + clientSentence);  
           capitalizedSentence = clientSentence.toUpperCase() + '\n'; 
           outToClient.writeBytes(capitalizedSentence); 
        } 
	
	}


} 

import java.io.*; 
import java.net.*; 

class TCPClient { 

		private String sentence,modifiedSentence; 
		private DataOutputStream outToServer;
		private BufferedReader inFromServer;
		private Socket clientSocket;
		private BufferedReader inFromUser;
		
		public TCPClient() throws Exception{
		
		inFromUser =  new BufferedReader(new InputStreamReader(System.in)); 
        clientSocket = new Socket("192.168.1.2", 6789); 
        outToServer = new DataOutputStream(clientSocket.getOutputStream()); 
        inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream())); 
       
		}
		
		public String getSentence()
		{
		return sentence;
		}
		
		public void setSentence(String str)
		{
			this.sentence=str;
		}
		
		
		
		public String getModifiedSentence()
		{
			return modifiedSentence;
		}
		
		public void setModifiedSentence(String str )
		{
			this.modifiedSentence=str;
		}
		
		public void run() throws Exception{
		
		
		System.out.println("Enter a String");
		sentence = inFromUser.readLine(); 
		
        outToServer.writeBytes(sentence + '\n'); 
        modifiedSentence = inFromServer.readLine(); 
        System.out.println("FROM SERVER: " + modifiedSentence); 
		
		TCPServer mySever = TCPServer.getInstance();/*This is the place where I try to access server object*/
        clientSocket.close(); 
		
		}
      
 } 

public class Server{
	public static void main(String[] args) throws Exception{
	  TCPServer x = TCPServer.getInstance();
	  x.run();
	}
}

public class Client{
	public static void main(String[] args) throws Exception{
	TCPClient client = new TCPClient();
	client.run();
	}
}