Error instantiating servlet class, HTTP Status 500 – Internal Server Error

I am new to Servlets. I have created a simple servlet by implementing Servlet Interface from youtube tutorials. This is my FirstServlet class implementing Servlet -

package com.servlets;

import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

import java.io.IOException;

public class FirstServlet implements Servlet {
    ServletConfig conf;

    @Override
    public void destroy() {
        // TODO Auto-generated method stub
        System.out.println("going to detroy object");
    }

    @Override
    public ServletConfig getServletConfig() {
        // TODO Auto-generated method stub

        return this.conf;
    }

    @Override
    public String getServletInfo() {
        // TODO Auto-generated method stub

        return "this servlet is created by Mayank Kumar";
    }

    @Override
    public void init(ServletConfig config) throws ServletException {
        // TODO Auto-generated method stub
        // TODO Auto-generated method stub
        this.conf = config;
        System.out.println("Creating object");

    }

    @Override
    public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
        // TODO Auto-generated method stub
        System.out.println("Servicing ...");
    }
}

I have declared my servlet in web.xml file -

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://xmlns.jcp.org/xml/ns/javaee"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
    id="WebApp_ID" version="4.0">
    <display-name>ServletandJSP</display-name>
    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.htm</welcome-file>
        <welcome-file>index.jsp</welcome-file>
        <welcome-file>default.html</welcome-file>
        <welcome-file>default.htm</welcome-file>
        <welcome-file>default.jsp</welcome-file>
    </welcome-file-list>

    <servlet>
        <servlet-name>first</servlet-name>
        <servlet-class>com.servlets.FirstServlet</servlet-class>
    </servlet>

    <!-- creating mapping -->
    <servlet-mapping>
        <servlet-name>first</servlet-name>
        <url-pattern>/web</url-pattern>
    </servlet-mapping>


</web-app>

I am using eclipse ide. I created a dynamic web project and have tomact 9 installed. Whenever I try to run my servlet(http://localhost:8080/ServletandJSP/web) this exception is coming - Type Exception Report

Message Error instantiating servlet class [com.servlets.FirstServlet]

Description The server encountered an unexpected condition that prevented it from fulfilling the request.

Exception

javax.servlet.ServletException: Error instantiating servlet class [com.servlets.FirstServlet] org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542) org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:687) org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:346) org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374) org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:887) org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1684) org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) java.base/java.lang.Thread.run(Unknown Source) Root Cause

java.lang.ClassNotFoundException: com.servlets.FirstServlet org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1364) org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1187) org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542) org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:687) org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:346) org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374) org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:887) org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1684) org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) java.base/java.lang.Thread.run(Unknown Source) Note The full stack trace of the root cause is available in the server logs.