Getting HTTP Status 400 error while running a Servlet class using Tomcat server

I am totally new to writing servlets. I have created a simple HelloWorld program, but while running the application I'm getting the following error:

HTTP Status 404 - /HelloWorld/HelloWorld

type Status report

message /HelloWorld/HelloWorld

description: The requested resource is not available.

Below is my code:

import java.io.IOException;import java.io.PrintWriter;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;@WebServlet("/HelloWorld")public class HelloWorld extends HttpServlet {    private static final long serialVersionUID = 1L;               public HelloWorld() {        super();      }        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        PrintWriter out=response.getWriter();        out.println("Hello World");    }}

And my web.xml

<display-name>HelloWorld</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></web-app>

I'm using Tomcat version:7.0 and my IDE is Eclipse Luna. Why is this error being thrown?