I am trying to use java socket, but netbeans does not see the main classes. Could someone please tell me what i am doing wrong?

Question

package doslab2_datagram;

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

class client {
public static void main(String args[]) throws Exception {
    Scanner scan = new Scanner(System.in);
    DatagramSocket clientSocket = new DatagramSocket();
    InetAddress IPAddress = InetAddress.getByName("localhost");
    byte[] sendData = new byte[1024];
    byte[] receiveData = new byte[1024];
    System.out.println("Enter the operator");
    String temp = scan.next();
    System.out.println("Enter the operand");
    String temp1 = scan.next();
    System.out.println("Enter the operand");
    String temp2 = scan.next();
    String sentence = temp + " " + temp1 + " " + temp2;
    sendData = sentence.getBytes();
    DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, 9876);
    clientSocket.send(sendPacket);
    DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
    clientSocket.receive(receivePacket);
    String modifiedSentence = new String(receivePacket.getData());
    System.out.println("FROM SERVER:" + modifiedSentence);
    clientSocket.close();
 }
}

---

package doslab2_datagram;

import java.io.*;
import java.net.*;
import java.util.*;
import java.math.*;

class server {
public static void main(String args[]) throws Exception {
    DatagramSocket serverSocket = new DatagramSocket(9876);
    byte[] receiveData = new byte[1024];
    byte[] sendData = new byte[1024];
    float sum = 0;
    while (true) {
        DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);

        serverSocket.receive(receivePacket);
        String sentence = new String(receivePacket.getData());
        System.out.println("RECEIVED: " + sentence);
        StringTokenizer st = new StringTokenizer(sentence);
        String str[] = new String[3];

        while (st.hasMoreTokens()) {
            for (int i = 0; i < 3; i++) {
                str[i] = (st.nextToken());
            }
        }
        for (int i = 0; i < 3; i++) {
            System.out.println("THE VALUE IS " + str[i]);
        }

        String operator = str[0];
        String operand1 = str[1];
        String operand2 = str[2];
        float f = Float.valueOf(operand1.trim()).floatValue();
        float f1 = Float.valueOf(operand2.trim()).floatValue();


        if (operator.equals("+")) {
            try {
                sum = f + f1;
            } catch (NumberFormatException nfe) {
                System.out.println("NumberFormatException: " + nfe.getMessage());
            }
        } else if (operator.equals("-")) {
            try {
                sum = f - f1;
            } catch (NumberFormatException nfe) {
                System.out.println("NumberFormatException: " + nfe.getMessage());
            }
        } else if (operator.equals("*")) {
            try {
                sum = f * f1;
            } catch (NumberFormatException nfe) {
                System.out.println("NumberFormatException: " + nfe.getMessage());
            }
        } else if (operator.equals("/")) {
            try {
                sum = f / f1;
            } catch (NumberFormatException nfe) {
                System.out.println("NumberFormatException: " + nfe.getMessage());
            }
        } else if (operator.equals("%")) {
            try {
                sum = f % f1;
            } catch (NumberFormatException nfe) {
                System.out.println("NumberFormatException: " + nfe.getMessage());
            }
        } else if (operator.equals("%")) {
            try {
                sum = (float) Math.pow(f, f1);
            } catch (NumberFormatException nfe) {
                System.out.println("NumberFormatException: " + nfe.getMessage());
            }
        }


        InetAddress IPAddress = receivePacket.getAddress();
        int port = receivePacket.getPort();
        String capitalizedSentence = String.valueOf(sum);
        sendData = capitalizedSentence.getBytes();
        DatagramPacket sendPacket =
                new DatagramPacket(sendData, sendData.length, IPAddress, port);
        serverSocket.send(sendPacket);
    }
 }
}