Simple Calculator using TCP in Java

The Internet Protocol suite contains all sort of protocols that enables communication between devices over the Internet. TCP is the most common protocol of this suite. It is a connection-oriented protocol, which means it maintains the established connection between two devices till the end of a communication. This is the reason it is used while web surfing, sending emails and transferring files.

In this article, we will develop a simple client-server side calculator using TCP in Java. The client will request the operation and the server will send the result to client device after calculating it.

Java Networking

Let’s briefly understand a few basic concepts first about Java networking −

InetAddress

An IP address is either a 32-bit or 128-bit unsigned number that uniquely identifies devices on Internet. It is easy to remember the name of IP host rather than the numerical address. So, we need to encapsulate this using ‘InetAddress’ class. We use its built-in method ‘getLcalHost()’ to retrieve the IP address of LocalHost.

Socket

It is the base of Java networking concept, it allows a device to serve various clients at once. There are two kinds of TCP socket classes. One is ‘ServerSocket’ class used for servers that receive and sends result to client device and the other one is ‘Socket’ class used on client side to request information.

I/O Streams

Stream is an abstraction that is used while performing Input and Output operations in Java networking. By using the ‘getInputStream()’ and ‘getOutputStream()’, we can access the input and output streams associated with ‘Socket’ class.

Program of Calculator using TCP

Program of Client Side

Working of code

• We first import the two most important packages named ‘java.net’ to access all the classes regarding Java networking and ‘java.io’ for input and output streams. The ‘java.util’ package to use ‘Scanner’ class.

• Fetch the LocalHost address and then, store the port number and address in the object of ‘Socket’ class.

• Define two objects named ‘inpStrm’ to receive data and ‘outpStrm’ to send the data in the form of streams.

• Now, inside the try block, we will ask for user input to request an operation and to receive the result accordingly.

Example

import java.io.*;
import java.net.*;
import java.util.*;
public class ClientCal {
   public static void main(String[] args) throws IOException {
      // fetching address of localhost
      InetAddress addr = InetAddress.getLocalHost();
      Scanner inp = new Scanner(System.in);
      // establishing socket connection
      Socket sock = new Socket(addr, 6666);
      // to send and receive data through streams
      DataInputStream inpStrm = new DataInputStream(sock.getInputStream());
      DataOutputStream outpStrm = new DataOutputStream(sock.getOutputStream());
      try {
         while (true) {
            System.out.println("Type 1 for Addition");
		   System.out.println("Type 2 for Subtraction");
		   System.out.println("Type 3 for Multiplication");
		   System.out.println("Type 4 for Division");
            System.out.println("Enter your choice: ");
            int oprtr = inp.nextInt();
            // Type 0 for cut the connection
            if (oprtr == 0) {
               break;
            }
            // sending the operator for operation
            outpStrm.writeInt(oprtr); 
            // reading result from server
            String res = inpStrm.readUTF();
            System.out.println("Your Result for the given operation = " + res);
         }
      }
      // to handle exception
      catch(Exception exp) {
         System.out.println(exp);
      } 
   }
}

Program of Server Side

Working of code

• First, establish a connection with the client.

• Then read the request from client side.

• Inside the try block, using switch case we perform the operation and send the result to client device.

• Catch block is used to handle any kind of exception during run time.

Example

import java.io.*;
import java.net.*;
import java.util.*; 
public class ServeCalc {
   public static void main(String args[]) throws IOException {
      // establishing the socket connection
      ServerSocket Serve = new ServerSocket(6666);
      Socket sock = Serve.accept();
      // to send and receive data through streams
      DataInputStream inpStrm = new DataInputStream(sock.getInputStream());
      DataOutputStream outpStrm = new DataOutputStream(sock.getOutputStream());
      try {
         while (true) {
            // reading input from client
            int oprtr = inpStrm.readInt();
            System.out.println("Client has requested for " + oprtr + " operation");
            int res = 0;
            int data1 = 15;
            int data2 = 5;
            switch(oprtr) {
	            case 1 : 
	               res = data1 + data2;
                  outpStrm.writeUTF(Integer.toString(res));
		            break;
	            case 2 :
		            res = data1 - data2;
                  outpStrm.writeUTF(Integer.toString(res));
		            break;
	            case 3 :
		            res = data1 * data2;
                  outpStrm.writeUTF(Integer.toString(res));
		            break;
	            case 4 :
		            res = data1 / data2;
                  outpStrm.writeUTF(Integer.toString(res));
		            break;
	            default :
		         outpStrm.writeUTF(" You have given invalid choice! ");
		            break; 
            }
            System.out.println("Result sent to the client...");
         }
      }
      // to handle exception
      catch(Exception exp) {
         System.out.println(exp);
      } 
   }
}

To run both programs, open two cmd simultaneously on your local machine. On first cmd interface, compile and run the server-side program and then on the other interface, execute the client-side program.

Output on Server side

D:\Java Programs>javac ServeCalc.java
D:\Java Programs>java ServeCalc
Client has requested for 1 operation
Result sent to the client...
Client has requested for 2 operation
Result sent to the client...
Client has requested for 3 operation
Result sent to the client...
Client has requested for 4 operation
Result sent to the client...
java.net.SocketException: Connection reset

Output on Client side

D:\Java Programs>javac ClientCal.java 
D:\Java Programs>java ClientCal
Type 1 for Addition
Type 2 for Subtraction
Type 3 for Multiplication
Type 4 for Division
Enter your choice:
1
Your Result for the given operation = 20
Type 1 for Addition
Type 2 for Subtraction
Type 3 for Multiplication
Type 4 for Division
Enter your choice:
2
Your Result for the given operation = 10
Enter your choice:
0

When we enter 0 the connection will get terminated and program will stop its execution.

Conclusion

In this article, we have learned about a few essential concepts of Java networking. Also, discussed server-side and client-side programs of a simple calculator using Transmission Control Protocol. We discovered how we could establish a connection between client and server devices in Java.