I'm trying to access the data from a single row fetched by a select query. When I try to access the data through rs.getString() it throws NullPointerException.  Any method to access the data from the result set leads to a NullPointerException. Why does this happen?  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {     doGet(request, response);      boolean status=true;     String email=request.getParameter("user");     String password=request.getParameter("pass");      PrintWriter pw = response.getWriter();      if (status) {         String driverName = "org.hsqldb.jdbcDriver";         String URL = "jdbc:hsqldb:hsql://localhost/";         String UID = "SA";         String PWD = "";         Connection con = null;         PreparedStatement sql = null;         ResultSet rs = null;          try {             Class.forName(driverName);             con = DriverManager.getConnection(URL, UID, PWD);              System.out.println("connected = " + con);              sql = con.prepareStatement("SELECT * FROM \"USER\" where email='"+email+"' and password='"+password+"'");             boolean sql_st=sql.execute();             System.out.println(sql_st);             rs=sql.getResultSet();              if(rs.next())             {                 HttpSession hp = request.getSession(true);                 rs=sql.getResultSet();                  hp.setAttribute("name", rs.getString("name"));                 pw.println("&lt;html&gt;&lt;body&gt;&lt;h1&gt;Welcome "+rs.getString("name")+"&lt;/h1&gt;&lt;/body&gt;&lt;/html&gt;");             }             else             {                 pw.println("&lt;html&gt;&lt;body&gt;&lt;h1&gt;invalid credentials&lt;/h1&gt;&lt;/body&gt;&lt;/html&gt;");                 pw.println("&lt;html&gt;&lt;body&gt;&lt;a href=login.html&gt;go back&lt;/a&gt;&lt;/body&gt;&lt;/html&gt;");             }         } catch (SQLException e) {             e.printStackTrace();         } catch (ClassNotFoundException e) {             e.printStackTrace();         }      }     else     {         pw.println("&lt;html&gt;&lt;body&gt;&lt;h1&gt;Invalid Input&lt;/h1&gt;&lt;/body&gt;&lt;/html&gt;");         pw.println("&lt;html&gt;&lt;body&gt;&lt;a href=register.html&gt;go back&lt;/a&gt;&lt;/body&gt;&lt;/html&gt;");     }
What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?
User is suspended network-wide, except not really A user has been active on one of the sites recently, even though they're concurrent suspended network-wide on the rest of the network. How is this possible, and is it possible to evade a network suspension on only one site? What is the best way to install Guest Additions with all the resize and clipboard and file sharing features on Ubuntu 16.04? How to extend the background of an image? Code Formating in Comments How to check battery temperature? How do I know the normal temperature of it?  My OS is Ubuntu, and my laptop is Lenovo G470.  Output of acpi -t:  Thermal 0: ok, 0.0 degrees C Let $G$ be a group and $\{H_i\}_{i\in I}$ a family of subgroups. I would like to find a condition that will imply that $\cup_{i\in I} H_i$ is a subgroup. I know that it's not true in general, I need help to find this condition.  Any help is welcome.  Thanks a lot. I want to create a animation like those "spacetime deformation" ones, but I am stuck on creating "spacetime".  (a mesh/plane).  I created a plane, gave it a soft body, collisions, and a passive rigidbody.    A cube with a rigidbody and collisions will land and deform the mesh, but it snaps right back.  How can I make it so the cube lands, and then leaves the plane deformed, and the cube just sits there?  I googled around and searched this site, nothing comes up.  An image of what I want (after it settles):    The ball depressed the mesh, creating an indentation. Lock in mysql database Ubuntu 20.04 run ok on Lenovo ThinkPad E15 laptop? question about the limit $\lim_{h\to0}\frac{\arcsin(x+h)-\arcsin(x)}{h}$ Add folder to PATH How to add something to PATH ? I have added like   PATH=$PATH:/home/example export PATH   and it works until I restart , after that when  I type env in PATH there is no /home/example. When I parent mesh to an armature (automatic weights), the mesh "jumps" forward a bit. If I select armature and switch to edit mode it "jumps" backward a bit.   Why is it happening and how can I fix it? I already applied location, rotation, and scale to the mesh and armature, but it didn't help.  Thank you in advance! DNS settings on managed switches in LAN We have a Windows 2008 server that is connected to a managed switch with about 15 Cat5e connections and three fiber branches that go to different parts of campus. At each of these parts there is another managed switch that branches out to the LAN. Our cable Internet comes into one of these locations, goes through the supplied modem and into a Sonicwall.  Question: Under DNS settings on all the switches, should I list the LAN Server IP and/or just the Gateway IP (Sonicwall)? How can I intercept XMLHttpRequests from a Greasemonkey script? What are the possible values of the Hibernate hbm2ddl.auto configuration and what do they do I really want to know more about the update, export and the values that could be given to hibernate.hbm2ddl.auto I need to know when to use the update and when not? And what is the alternative?  These are changes that could happen over DB:   new tables new columns in old tables columns deleted data type of a column changed a type of a column changed its attributes tables dropped values of a column changed    In each case what is the best solution? How can I use multiple overlay effects simultaneously in Photoshop? There are 3 overlay effects available in Photoshop as layer styles: Color, Gradient and Pattern. The problem: these effects come in a strictly fixed order!  Is it possible to make a translucent Gradient Overlay over a Color Overlay using only layer styles? Or a Multiply Pattern and Color Overlays? Did Luke attempt to retake the Jedi Temple on Coruscant? After the New Republic gains control of Coruscant through the Galactic Concordance, did Luke Skywalker attempt to reclaim (or even visit) the former and still very much intact Jedi Temple, now converted to be the deceased Emperor's palace?   If Luke is so insistent on saving a tree just because it belongs to the Jedi and the Empire stole it, then shouldn't reclaiming the Jedi Temple be even higher priority?  If he did, is he aware of the Sith shrine beneath it? Which is something even Yoda does not know. And if he didn't, why didn't he? How to use if-else option in JSTL E: Package 'guile-1.8-dev' has no installation candidate this is an error i got I have apt-get 0.7.23.1 on host machine. I do not have root, thus not able to update it, or install other packages.  I want to download .deb packages with it, but neither  apt-get -d bash   (Invalid operation bash)  nor  apt-get -d install bash   (do not have root)  work.  On my home machine with a newer version of apt-get I can  apt-get download bash   and it does exactly what I want it to.  How can I perform the same on the host machine? If $z_{1},z_{2},z_{3}$ are three complex number Such that $|z_{1}| = 2\;\;,|z_{2}| = 3\;\;, |z_{3}| = 4\;\;$ Then $\max$ of $|z_{1}-z_{2}|^2+|z_{2}-z_{3}|^2+|z_{3}-z_{1}|^2$  $\bf{My\; Try::}$ Let $z_{1}=2\left(\cos \alpha+i\sin \alpha\right)$ and $z_{2}=3\left(\cos \beta+i\sin \beta\right)$ and $z_{3}=4\left(\cos \gamma+i\sin \gamma\right)$ So $$f(\alpha,\beta,\gamma) = 58-\left[12\cos(\alpha-\beta)+24\cos(\beta-\gamma)+16\cos(\gamma-\alpha)\right]$$ Now How can I calculate $\max$ of $f(\alpha,\beta,\gamma)$ Help me Thanks