ping <hostname> - to test

ipconfig(for windows)/ifconfig(linux) - to get network configuration

netstat - statistical report

nslookup - DNS lookup name

// Java Program to Illustrate Creation of ConnectException

// Importing required classes
import java.io;
import java.net.*;
import java.util.*;

// Main class
// To test hostname and port connectivity
public class GFG {

    // Main driver method
    public static void main(String[] args)
    {

        // Hostname is defined so do have arbitrary
        // localhost value which is nothing but 127.0.0.1
        String hostname = "127.0.0.1";

        // PORT is defined here
        // It should have been 8080 or 8000 but cannot be 80

        // If IP and PORT is invalid it will get exception
        // Trying to connect
        int port = 80;

        // Try block to check for exceptions
        try (Socket socket = new Socket(hostname, port)) {

            // InputStream to read data from socket
            InputStream inputStream
                = socket.getInputStream();
            InputStreamReader inputStreamReader
                = new InputStreamReader(inputStream);

            int data;

            StringBuilder outputString
                = new StringBuilder();

            // Data read from input stream
            while ((data = inputStreamReader.read())
                   != -1) {
                outputString.append((char)data);
            }
        }

        // Catch block to handle the exceptions
        catch (IOException ex) {

            // If the given hostname and port number are
            // invalid, connectivity cannot be established
            // and hence error thrown Exception will happen
            // when socket will not reachable
            System.out.println(
                "Connection Refused Exception as the given hostname and port are invalid : "
                + ex.getMessage());
        }
    }
}

// Java Program to Demonstrate DB Connection Setup

// Importing basic libraries
import java.io.*;
import java.util.*;

// Step 1: Importing DB
import java.sql.*;

// Try block to check for exceptions
try {

    // Setting initial connection object to null
    Connection con = null;

    String driver = "com.mysql.jdbc.Driver";

    // Step 2: Loading and registering drivers

    // Here if IP address is not your localhost,
    // need to specify that or specific address
    String IPADDRESS = "localhost"

        // 3306 is port number
        String url1
        = "jdbc:mysql://IPADDRESS:3306/";

    // If noy suggesting that to assign generally is
    // followed as DB = mySQL username= root, password=1234
    String db = "<your dbname>";
    String dbUser = "<username>";
    String dbPasswd = "<password>";

    // Loading driver using forName() method
    Class.forName(driver).newInstance();
    // Registering driver using DriverManager
    con = DriverManager.getConnection(url1 + db, dbUser,
                                      dbPasswd);

    // Display message on the console
    // when the connection is successfully setup
    System.out.println("Database Connection Established");
}

// Catch block to handle the exceptions
catch (IOException ex) {

    // Exception will happen when the IPAddress and port
    // number are mismatch By pinging, we can correct that

    // Display message on the console and
    // getting exception message using getMessage() method
    System.out.println(
        "Connection Refused Exception as the given hostname and port are invalid : "
        + ex.getMessage());
}