什么是单例Java类，您能告诉我Servlet类是否是单例类？

Question

import java.io.*;

导入javax.servlet。; 导入java.util。;

公共类FirstServlet扩展了GenericServlet {     公共无效init（）引发ServletException {}

@Override
public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {

//set response content type
    res.setContentType("text/html");
    //get PrinterWriter Object
    PrintWriter pw=res.getWriter();
    //write response
    Date d=new Date();
    try {
        Thread.sleep(40000);

    } catch (Exception e) {
        // TODO: handle exception
    }
    pw.println("<br>our servlet class(Date Servlet); object hashcode "+this.hashCode());
    pw.println("<br> request object hash code"+this.hashCode());
    pw.println("<br> response object hashcode"+res.hashCode());
    pw.println("<br>current thread hashcode"+res.hashCode());
    pw.println("<b><i><center>Date and Time is "+d+" </b></i></center>");
    pw.println("Welcome to servlet programming");
    //close stream
    pw.close();

}//service(-,-)

} //班