Client/server expression evaluation in JAVA

Question

I have created a simple client server application using TCP. I am using eclipse and am pretty much new to TCP, so my questions: 1)If i want the client to send an expression such as "10+20-5" so i put it in the argument? which is arg[0]. 2)After sending such an expression mentioned above how do I make the server calculate this actual expression so as to return back to the client the result "25"?

Client Code:

public class TCPClient {
public static void main (String args[]) { 
   // arguments supply message and hostname
    Socket s = null;
    try{
        int serverPort = 7896;
        s = new Socket(args[1],serverPort);

        DataInputStream in =new DataInputStream(s.getInputStream());
        DataOutputStream out = new DataOutputStream(s.getOutputStream());

        out.writeUTF(args[0]);
        String data = in.readUTF(); 
        System.out.println("Received: "+ data) ;
        }catch (UnknownHostException e) {System.out.println("Socket:"+e.getMessage());
        }catch (EOFException e){System.out.println("EOF:"+e.getMessage());
        }catch (IOException e){System.out.println("readline:"+e.getMessage());
        }finally {if(s!=null) 
        try {s.close(); 
        }catch (IOException e) {System.out.println ("close:" + e.getMessage());}
    }
}

}

Server Code:

public class TCPServer {
public static void main (String args[]) {
    try{
        int serverPort = 7896; // the server port
        ServerSocket listenSocket = new ServerSocket(serverPort);
        while(true) {
        System.out.println("Server is ready and waiting for requests ... ");
            Socket clientSocket = listenSocket.accept();
            Connection c = new Connection(clientSocket);

        }
        } catch(IOException e) {System.out.println("Listensocket:"+e.getMessage());}
}
}

class Connection extends Thread {
DataInputStream in;
DataOutputStream out;
Socket clientSocket;

public Connection (Socket aClientSocket) {
        try {
        clientSocket = aClientSocket;
        in = new DataInputStream( clientSocket.getInputStream());
        out =new DataOutputStream( clientSocket.getOutputStream());

        this.start();
        } catch(IOException e) {System.out.println("Connection:"+e.getMessage());}
}

public void run(){
        try {   
            String data = in.readUTF();  
            out.writeUTF(data);
        }catch (EOFException e){System.out.println("EOF:"+e.getMessage());
        } catch(IOException e) {System.out.println("readline:"+e.getMessage());
        } finally{ try {clientSocket.close();}catch (IOException e){/*close failed*/}}
}
}

Answer 1

1/ In java, when you pass java youclass_or_jar_file argument argument

Then the argument[0] will be you your first argument you typed, not the program name as in C/C++ . So in this situation, you can use the argument vector in the format as [host, port, "message"] . Then in your program, you just send your arg[2] in this case is the message

2/To evaluate the received expression, you should have implemented the evaluation method yourself.

In this method, in my opinion you should parse the input into the postfix notation http://en.wikipedia.org/wiki/Reverse_Polish_notation , by using stack , read the wiki for more infomation then evaluate it.

Hope this help