I am trying to implement SVM classifier in Java using libsvm. I am getting the following error:  Exception in thread "main" java.lang.NullPointerException at libsvm.Kernel.dot(svm.java:213) at libsvm.Kernel.kernel_function(svm.java:172) at libsvm.SVC_Q.&lt;init&gt;(svm.java:1161) at libsvm.svm.solve_c_svc(svm.java:1333) at libsvm.svm.svm_train_one(svm.java:1510) at libsvm.svm.svm_train(svm.java:2067)   I am trying to implement a binary classifier on 6 training examples: this is my code:  import libsvm.*;  import java.io.*; import java.io.Reader; import java.lang.Object;   public class SVMclassifier {     public SVMclassifier(){          svm_problem svmData=new svm_problem();         svmData.l=6;         double[] lab={1,0,1,1,0,0};         svmData.y=lab;          svm_node[][] values=new svm_node[6][3];          System.out.print("I am here");         svm_node AA=new svm_node();         AA.index=1;         AA.value=0.1;         values[0][1]=AA;         AA.index=1;         AA.value=0.9;         values[0][2]=AA;         AA.index=1;         AA.value=0.9;         values[1][0]=AA;         AA.index=2;         AA.value=0.1;         values[1][1]=AA;         AA.index=1;         AA.value=0.05;         values[2][0]=AA;         AA.index=2;         AA.value=0.95;         values[2][1]=AA;         AA.index=1;         AA.value=0.06;         values[3][0]=AA;         AA.index=2;         AA.value=0.90;         values[3][1]=AA;         AA.index=1;         AA.value=0.95;         values[4][0]=AA;         AA.index=2;         AA.value=0.05;         values[4][1]=AA;         AA.index=1;         AA.value=0.90;         values[5][0]=AA;         AA.index=2;         AA.value=0.06;         values[5][1]=AA;          svmData.x=values;          svm_model paras=new svm_model();          svm_parameter params =new svm_parameter();         int[] bb={1,1,1};         double[] cc={1,1,1};         System.out.println("I am here");         params.svm_type = svm_parameter.C_SVC;         params.kernel_type = svm_parameter.LINEAR;         params.degree = 3;         params.gamma = 0.5;   // 1/num_features         params.coef0 = 0;         params.nu = 0.5;         params.cache_size = 100;         params.C = 1;         params.eps = 1e-3;         params.p = 0.1;         params.shrinking = 1;         params.probability = 0;         params.nr_weight = 0;         params.weight_label=bb;         params.weight=cc;         paras=svm.svm_train(svmData, params) ;           for(int i=0;i&lt;=5;i=i+1){             svm_node[] v=values[i];             double u=svm.svm_predict(paras, v);             System.out.println(u);               }     }      public static void main(String[] args) {         // TODO Auto-generated method stub         SVMclassifier A=new SVMclassifier();     } }   I am new to java as well as libsvm. any help would be welcome. Thanks
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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?
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This code throws a NullReferenceException when it calls ExecuteScalar:  selectedPassengerID = 0;  //SqlCommand command = GenericDataAccess.CreateCommand();   // 2nd test string connectionString = ""; SqlConnection conn;  connectionString = ConfigurationManager.     ConnectionStrings["ConnST-MHM"].ConnectionString; conn = new SqlConnection(connectionString); SqlCommand command = new SqlCommand(); command.CommandType = CommandType.StoredProcedure ; command.Connection = conn; command.CommandText = "SearchForPassenger";  SqlParameter param;  param = command.CreateParameter(); param.ParameterName = "@name"; param.Value = pName; // Session[""]; param.DbType = DbType.String; command.Parameters.Add(param);  param = command.CreateParameter(); param.ParameterName = "@flightDate"; param.Value = date;  param.DbType = DbType.String; command.Parameters.Add(param);  param = command.CreateParameter(); param.ParameterName = "@ticketNo"; param.Value = ticketNumber;  param.DbType = DbType.Int32; command.Parameters.Add(param);  int item;  command.Connection.Open(); item = (int)command.ExecuteScalar();
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This is the error I get when I run my web application in an instance of the Tomcat servlet container started by NetBeans. To fix this I even changed the heap size in netbeans.conf, but still it shows the same error. How can I keep this from happening?   HTTP Status 500 -   --------------------------------------------------------------------------------  type Exception report  message   description The server encountered an internal error () that prevented it from fulfilling this request.  exception   javax.servlet.ServletException: Servlet execution threw an exception     org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:362)   root cause   java.lang.OutOfMemoryError: Java heap space  note The full stack trace of the root cause is available in the Apache Tomcat/5.5.9 logs.
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I am trying to fit a SVM to my data. My dataset contains 3 classes and I am performing 10 fold cross validation (in LibSVM):   ./svm-train -g 0.5 -c 10 -e 0.1 -v 10 training_data   The help thereby states:  -c cost : set the parameter C of C-SVC, epsilon-SVR, and nu-SVR (default 1)   For me, providing higher cost (C) values gives me higher accuracy. What does C in SVM actually mean? Why and when should I use higher/lower values (or the LibSVM given default value) of C?
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What would you consider to be the best exception type to throw when an extension method is called on a null instance (where the extension method does not allow it)? Since extension methods are nothing but static methods you could argue that it should be ArgumentNullException, but on the other hand they're used like instance methods so it might be more natural to use the NullReferenceException. Let's take the following example:  public static string ToInvariantString(this IFormattable value, string format) {     return value.ToString(format, CultureInfo.InvariantCulture); }   This way a NullReferenceException will be thrown if the value parameter is null.   The other example would be:  public static string ToInvariantString(this IFormattable value, string format) {     if (value == null) throw new ArgumentNullException("value");     return value.ToString(format, CultureInfo.InvariantCulture); }   EDIT: In some of the answers you have pointed out that an extension methods can be called like a static method and in those cases a null reference exception would be wrong, which is a great point, and actually one of my concerns, not sure why I forgot to mention that in the question in the first place.   Someone also pointed out that it's wrong to throw a NullReferenceException, and yes, it is. That's why I don't throw it, I just let it happen (let the CLR throw it) by not guarding the method.  I think I favor the ArgumentNullException (that's what I've use so far) but I still think there is at least room to argue for an against the NullReferenceException since it seems more natural in most places where the method is going to be used.
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In a SVM with linear kernel, could you explain to me what exactly the C parameter is/represents?  An example why it's important to select a good value for C would also be appreciated.  Thank you.
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When modelling classes, what is the preferred way of initializing:   Constructors, or Factory Methods   And what would be the considerations for using either of them?  In certain situations, I prefer having a factory method which returns null if the object cannot be constructed. This makes the code neat. I can simply check if the returned value is not null before taking alternative action, in contrast with throwing an exception from the constructor. (I personally don't like exceptions)  Say, I have a constructor on a class which expects an id value. The constructor uses this value to populate the class from the database. In the case where a record with the specified id does not exist, the constructor throws a RecordNotFoundException. In this case I will have to enclose the construction of all such classes within a try..catch block.  In contrast to this I can have a static factory method on those classes which will return null if the record is not found.  Which approach is better in this case, constructor or factory method?
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I was experimenting with C++ and found the below code as very strange.   class Foo{ public:     virtual void say_virtual_hi(){         std::cout &lt;&lt; "Virtual Hi";     }      void say_hi()     {         std::cout &lt;&lt; "Hi";     } };  int main(int argc, char** argv) {     Foo* foo = 0;     foo-&gt;say_hi(); // works well     foo-&gt;say_virtual_hi(); // will crash the app     return 0; }   I know that the virtual method call crashes because it requires a vtable lookup and can only work with valid objects.   I have the following questions    How does the non virtual method say_hi work on a NULL pointer? Where does the object foo get allocated?   Any thoughts?
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I am using java language,I have a method that is supposed to return an object if it is found. If it is not found, should I:  return null throw an exception other  Which is the best practise or idiom?
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When a Java VM crashes with an EXCEPTION_ACCESS_VIOLATION and produces an hs_err_pidXXX.log file, what does that indicate? The error itself is basically a null pointer exception. Is it always caused by a bug in the JVM, or are there other causes like malfunctioning hardware or software conflicts?  Edit: there is a native component, this is an SWT application on win32.
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I tried it and the errors are:  Exception in thread "main" java.awt.AWTError: Assistive Technology not found: org.GNOME.Accessibility.AtkWrapper at java.desktop/java.awt.Toolkit.newAWTError(Toolkit.java:472) at java.desktop/java.awt.Toolkit.fallbackToLoadClassForAT(Toolkit.java:488) at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:183) at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:177) at java.base/java.util.HashMap$KeySpliterator.forEachRemaining(HashMap.java:1608) at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484) at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474) at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:150) at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:173) at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:497) at java.desktop/java.awt.Toolkit.loadAssistiveTechnologies(Toolkit.java:532) at java.desktop/java.awt.Toolkit.getDefaultToolkit(Toolkit.java:613) at java.desktop/javax.swing.UIManager.getSystemLookAndFeelClassName(UIManager.java:660) at com.cburch.logisim.gui.start.Startup.parseArgs(Startup.java:250) at com.cburch.logisim.Main.main(Main.java:32)   The error seems to be...     Caused by: java.lang.ClassNotFoundException: org.GNOME.Accessibility.AtkWrapper       at  java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:582)       at   java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:190)       at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:499)       at java.base/java.lang.Class.forName0(Native Method)       at java.base/java.lang.Class.forName(Class.java:374)       at java.desktop/java.awt.Toolkit.fallbackToLoadClassForAT(Toolkit.java:485)       ... 14 more     OUTPUT for  apt-cache policy logicsim logisim  logisim:   Installed: 2.7.1~dfsg-1   Candidate: 2.7.1~dfsg-1   Version table:  *** 2.7.1~dfsg-1 500         500 http://in.archive.ubuntu.com/ubuntu bionic/universe amd64 Packages         500 http://in.archive.ubuntu.com/ubuntu bionic/universe i386 Packages         100 /var/lib/dpkg/status N: Unable to locate package logicsim   OUTPUT for update-java-alternatives -l  java-1.11.0-openjdk-amd64      1101       /usr/lib/jvm/java-1.11.0-openjdk-amd64 java-1.8.0-openjdk-amd64       1081       /usr/lib/jvm/java-1.8.0-openjdk-amd64
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I need help. I am currently trying to test this code before uploading  public class CoreValuesExt { ApexPages.StandardController sc; public boolean readonly {get; set;} public Core_Values__c cv {get; set;} public integer countEdit = 1; public string buttonValue {get; set;} public integer recordScan;  public CoreValuesExt(ApexPages.StandardController sc) {     this.sc = sc;     cv = new Core_Values__c();     cv.Account__c = sc.getid();      readonly = true;     buttonValue = 'Edit';     recordScan = [SELECT COUNT() FROM Core_Values__c WHERE Account__c = :cv.Account__c];    if (recordScan != 0){    cv = [SELECT id, HSE__c, Professionalism_Integrity__c, Quality_Accuracy__c, Technology_Innovation__c, Timeliness__c, Value_for_money__c FROM Core_Values__c WHERE Account__c = :cv.Account__c];     }  }  public ApexPages.PageReference Save() {     return sc.Save(); }  public void ApplyAction() {     countEdit++;     Integer modolus = Math.mod(countEdit, 2);     String total = cv.HSE__c + cv.Professionalism_Integrity__c + cv.Quality_Accuracy__c + cv.Technology_Innovation__c + cv.Value_for_Money__c + cv.Timeliness__c;     if(modolus == 0)     {         readonly = false;         buttonValue = 'Save';     }     else     {         if(total != 'nullnullnullnullnullnull')            {         if (recordScan == 0){         insert cv;         readonly = true;         buttonValue = 'Edit';         }         else         {         update cv;         readonly = true;         buttonValue = 'Edit';         }         }     }    }   }  With this trigger.  trigger CoreValuesTrigger on Core_Values__c (before insert) {  Core_Values__c cvs = Trigger.new; CoreValuesExt.ApplyAction(cvs);  }   But when I try to save, I get a message saying:      Illegal assignment from List to   CoreValuesExt__Core_Values__c at line 3 column 1   "  How do I go through with this? I need help. Thanks
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Looking for reviewers to suggest optimization and improvements, and to evaluate coding practices.  final class Variables {     private final int x;     private final int y;      Variables(int x2, int y2) {         this.x = x2;         this.y = y2;     }      public int getX() {         return x;     }      public int getY() {         return y;     }      @Override public String toString()  {          return "x = " + x + " y = " + y;     } }  public final class FindMissing {      private FindMissing() {};      /**  * Takes an input a sorted array with two variables that repeat in the  * range. Remaining variable are consecutive. and returns two variables that repeats  *   * eg: for a range of 1,2,3,4, a valid input is [1, 4], [1, 3] etc.  *   * @param a : the sorted array.  */ /*  * Why is start needed ?  * If start is not given then if a1 is empty how do we know if missing numbers were  * [1, 2] or [4, 5] ??.   */ public static Variables sortedConsecutiveTwoMissing (int[] a, int startOfRange) {     if (a == null) throw new NullPointerException("a1 cannot be null. ");      int low = startOfRange;     // calculating the highest value of the range. it needs to be 2 more than length since all elememts are consecutive.     int high = startOfRange + (a.length - 1) + 2;      int i = 0;     boolean foundX = false;     int x = 0;       while (i &lt; a.length) {         if (a[i] != low) {             if (foundX) {                 return new Variables(x, low);             } else {                 x = low;                 foundX = true;             }         } else {             i++;         }         low++;     }      return new Variables(x, high);  }  public static void main(String[] args) {         // unsortedConsecutiveTwoMissing         int[] a6 = {1, 4};         System.out.println("Expected 2 and 3, Actual " + sortedConsecutiveTwoMissing(a6, 1));         // unsortedConsecutiveTwoMissing         int[] a7 = {-4, -1};         System.out.println("Expected -3 and -2, Actual " + sortedConsecutiveTwoMissing(a7, -4));         int[] a8 = {-4, -3, -2, -1};         System.out.println("Expected 0 and 1, Actual " + sortedConsecutiveTwoMissing(a8, -4));         int[] a9 = {5};         System.out.println("Expected 4 and 6, Actual " + sortedConsecutiveTwoMissing(a9, 4));         }      }
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Consider this:  public class TestClass {      private String a;     private String b;      public TestClass()     {     a = "initialized";     }      public void doSomething()     {     String c;          a.notify(); // This is fine     b.notify(); // This is fine - but will end in an exception     c.notify(); // "Local variable c may not have been initialised"     }  }   I don't get it. "b" is never initialized but will give the same run-time error as "c", which is a compile-time error. Why the difference between local variables and members?  Edit: making the members private was my initial intention, and the question still stands...
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I am trying to start share-point workflow using CSOM(Client side object model) by following means of code. But i got the following error from the line mark in comment. Please help me to figure out this error.     Error :- Cannot invoke method or retrieve property from null   object. Object returned by the following call stack is null.   "GetWorkflowDeploymentService new   Microsoft.SharePoint.WorkflowServices.WorkflowServicesManager() "    public bool StartWorkFlow()  {     string workflowName = "UpdateDealStatus";     // connect to the workflow services via a CSOM client context    var workflowServicesManager = new WorkflowServicesManager(_sharepoint,                  _sharepoint.Web);    // connect to the deployment service    var workflowDeploymentService = workflowServicesManager.GetWorkflowDeploymentService();    // get all installed workflows   var publishedWorkflowDefinitions =    workflowDeploymentService.EnumerateDefinitions(true);             _sharepoint.Load(publishedWorkflowDefinitions);     try    {       _sharepoint.ExecuteQuery();//Error thrown from this line    }    catch (Exception ex)    {      }     // find the first workflow definition    var firstWorkflowDefinition = publishedWorkflowDefinitions.First();     // connect to the subscription service    var workflowSubscriptionService = workflowServicesManager.GetWorkflowSubscriptionService();     // get all workflow associations    var workflowAssociations = workflowSubscriptionService.EnumerateSubscriptionsByDefinition(firstWorkflowDefinition.Id);     _sharepoint.Load(workflowAssociations);    _sharepoint.ExecuteQuery();     foreach (var association in workflowAssociations)    {        Console.WriteLine("{0} - {1}",        association.Id, association.Name);    }     return true; }
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I am trying to download Minecraft 1.12 but as soon as it starts up and the launcher disappears, it crashes. I tried with a few other snapshots for 1.12 as well. Here is the crash report:  Exception in thread "main" java.lang.UnsupportedClassVersionError: net/minecraft/client/main/Main : Unsupported major.minor version 52.0     at java.lang.ClassLoader.defineClass1(Native Method)     at java.lang.ClassLoader.defineClassCond(ClassLoader.java:637)     at java.lang.ClassLoader.defineClass(ClassLoader.java:621)     at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)     at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)     at java.net.URLClassLoader.access$000(URLClassLoader.java:58)     at java.net.URLClassLoader$1.run(URLClassLoader.java:197)     at java.security.AccessController.doPrivileged(Native Method)     at java.net.URLClassLoader.findClass(URLClassLoader.java:190)     at java.lang.ClassLoader.loadClass(ClassLoader.java:306)     at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)     at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
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Eclipse is giving me a warning of the following form:     Type safety: Unchecked cast from Object to HashMap   This is from a call to an API that I have no control over which returns Object:  HashMap&lt;String, String&gt; getItems(javax.servlet.http.HttpSession session) {   HashMap&lt;String, String&gt; theHash = (HashMap&lt;String, String&gt;)session.getAttribute("attributeKey");   return theHash; }   I'd like to avoid Eclipse warnings, if possible, since theoretically they indicate at least a potential code problem.  I haven't found a good way to eliminate this one yet, though.  I can extract the single line involved out to a method by itself and add @SuppressWarnings("unchecked") to that method, thus limiting the impact of having a block of code where I ignore warnings.  Any better options?  I don't want to turn these warnings off in Eclipse.  Before I came to the code, it was simpler, but still provoked warnings:  HashMap getItems(javax.servlet.http.HttpSession session) {   HashMap theHash = (HashMap)session.getAttribute("attributeKey");   return theHash; }   Problem was elsewhere when you tried to use the hash you'd get warnings:  HashMap items = getItems(session); items.put("this", "that");  Type safety: The method put(Object, Object) belongs to the raw type HashMap.  References to generic type HashMap&lt;K,V&gt; should be parameterized.