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POJava problem with servlet and stacktrace thrown
 

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  1. POJava problem with servlet and stacktrace thrown
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    <p>I have the following in which I have to write a servlet that takes an age, marital status, house income and number of kids, goes out to a DB, and then returns the updated averages to the user. However, I am encountering this stacktrace:</p> <pre><code>java.lang.NullPointerException at HouseSurvey$SurveyResults.access$200(HouseSurvey.java:86) at HouseSurvey.doPost(HouseSurvey.java:43) at javax.servlet.http.HttpServlet.service(HttpServlet.java:709) at javax.servlet.http.HttpServlet.service(HttpServlet.java:802) at org.apache.catalina.servlets.InvokerServlet.serveRequest(InvokerServlet.java:419) at org.apache.catalina.servlets.InvokerServlet.doPost(InvokerServlet.java:169) at javax.servlet.http.HttpServlet.service(HttpServlet.java:709) at javax.servlet.http.HttpServlet.service(HttpServlet.java:802) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:868) at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:663) at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527) at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80) at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684) at java.lang.Thread.run(Unknown Source) </code></pre> <p>What the heck does this all mean? I figure I am getting a <code>NullPointerException</code>, but I don't see where. Here is my prog.:</p> <pre><code>import java.text.DecimalFormat; import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class HouseSurvey extends HttpServlet { private final static String SURVEY_FILE = "HouseSurvey.dat"; SurveyResults results; Household h; DecimalFormat form = new DecimalFormat("#,###,#00.00"); public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { PrintWriter out = response.getWriter(); //make a printwriter to print the page File survey = new File(SURVEY_FILE); if(!survey.exists()) //check to see if the file exists results = new SurveyResults(); else { //If the file exists, read it the latest survey tallies try { ObjectInputStream ips = new ObjectInputStream(new FileInputStream(survey)); results = (SurveyResults)ips.readObject(); //read the file into 'results' ips.close(); //close the input stream } catch(ClassNotFoundException e) {e.printStackTrace();} catch(FileNotFoundException f) {f.printStackTrace();} catch(IOException ioe) {ioe.printStackTrace();} } int ageValue = Integer.parseInt(request.getParameter("age")), childValue = Integer.parseInt(request.getParameter("children")); double incomeValue = Double.parseDouble(request.getParameter("income")); Boolean marriedValue = true; if (request.getParameter("status").equals("married")) marriedValue = true; else if(request.getParameter("status").equals("single")) marriedValue = false; Household h = new Household(ageValue,childValue,incomeValue,marriedValue); results.totalResults(h); //Write results to disk. try { ObjectOutputStream ops = new ObjectOutputStream(new FileOutputStream(survey)); ops.writeObject(results); ops.flush(); ops.close(); } catch(IOException ioe) {ioe.printStackTrace();} response.setContentType("text/html"); //contnent type for the responding webpage out.println("&lt;html&gt;\n"+ "&lt;head&gt;&lt;title&gt;Thanks!&lt;/title&gt;&lt;/head&gt;"+ "&lt;body style='background:cyan;'&gt;"+ " &lt;h1 style='text-align:center'&gt;RRC BIT Department - Household Survey&lt;/h1&gt;"+ " &lt;hr&gt;&lt;br/&gt;"+ " &lt;h2 style='text-align:center'&gt;Up to Date Survey Results&lt;/h2&gt;"+ " &lt;h4 style='margin-left:200px'&gt;Average Age: "+form.format(results.getAvgAge())+"&lt;/h4&gt;"+ " &lt;h4 style='margin-left:200px'&gt;Average Number of Children: "+form.format(results.getAvgKids())+"&lt;/h4&gt;"+ " &lt;h4 style='margin-left:200px'&gt;Average Number of Married Respondents: "+form.format(results.getTotalMarried())+"&lt;/h4&gt;"+ " &lt;h4 style='margin-left:200px'&gt;Average Number of Single Respondents: "+form.format(results.getTotalSingle())+"&lt;/h4&gt;"+ " &lt;h4 style='margin-left:200px'&gt;Average Income: "+form.format(results.getAvgIncome())+"&lt;/h4&gt;&lt;/body&gt;"); } private class Household { private int age, children; private double income; private boolean married=false; /**Method: Household * Constructor * @ param age - age of person surveyed:int * @ param children - number of children person surveyed has:int * @ param married - true or false, used to determine married or single:boolean * @ param income - the family income of the person surveyed:double */ private Household(int age, int children, double income, boolean married) { this.age=age; this.children=children; this.income=income; this.married=married; } //Getters private int getAge() {return age;} private int getChildren() {return children;} private double getIncome() {return income;} private boolean getMarried() {return married;} } private class SurveyResults implements Serializable { private double totalAge, totalChildren, totalMarried, totalSingle, totalIncome; /**Method: SurveyResults * Used for totals * @ param h - Household object created above:Household */ private void totalResults(Household h) { totalAge += h.getAge(); totalChildren += h.getChildren(); totalIncome += h.getIncome(); if(h.getMarried()) totalMarried += 1; else totalSingle += 1; } private double getTotalHouseholds() {return totalSingle + totalMarried;} private double getAvgAge() {return totalAge/getTotalHouseholds();} private double getAvgKids() {return totalChildren/getTotalHouseholds();} private double getTotalMarried() {return totalMarried;} private double getTotalSingle() {return totalSingle;} private double getAvgIncome() {return totalIncome/getTotalHouseholds();} } } </code></pre> <p>Originally in my HTML output, I accidentally had the line</p> <pre><code>"Average Number of Married Respondents: "+form.format(results.getTotalMarried())+"&lt;/h4&gt;" </code></pre> <p>as</p> <pre><code>"Average Number of Married Respondents: "+form.format(results.getAvgKids())+"&lt;/h4&gt;" </code></pre> <p>and that worked fine. Then I switched it to the former to get the totalMarried, and now it is giving me the exception. Where is the issue?</p> <p>Thanks in advance.</p>
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    2. COOh, sorry, line 89 is 'private class SurveyResults implements Serializable' and line 46 is ' results.totalResults(h);'
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    3. COIs that the entire stack trace, or just the top of it?
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