java,polymorphism,superRelated issues-Collection of common programming errors

• 
  mihi
  java jni instrumentation native-methods javaagents
  I am trying to write a Java agent library that is loaded dynamically via attach api to retransform some methods (those that appear in stack traces of certain threads) for recording method entry/exit. The method entry/exit information is then exported via a custom MBean.My current “prototype” works so far, as long as the instrumented methods are not native.According to the documentation of java.lang.instrument.Instrumentation#setNativeMethodPrefix(), it should be possible for java agents to repla
• 
  paiego
  mysql java mysql-cluster
  I’m trying to create a JPA Client for a MySQL Cluster 7.3. (MySQL 5.6).I’m building the jpa client on OS-X and have copied the libndbclient.so.6.0.0 and libndbclient_static.a from the Cluster SQL node on Linux.When I run the following code:EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory(“clusterdb”);EntityManager em = entityManagerFactory.createEntityManager();… the second line causes the following error to be produced.SEVERE: Attempt to load native library n
• 
  Luv
  java android opencv camera
  Hye there! I am new to OpenCV but somehow good at Android. I just need to know how can I open the Android native Camera using the OpenCV. I have been searching for a tutorial to get the hints but being failing since last three days! I just need the hints for being successful. Here, is a piece of code I’m using:button.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View arg0) {if(!openCamera()){txt.setText(“CAMERA NOT READY”);return;}}});this method should open the cam
• 
  Mihai
  java c++ jvm jni
  I am developing a Java application that calls a native dll library. My code for the c++ method that I call:JNIEXPORT jobjectArray JNICALL Java_Surf_TopSurfWrapp_computeSurfExtractDescriptor__LSurf_TopSurfVisualword_2Ljava_lang_String_2(JNIEnv *env, jclass c, jobject vw, jstring imagePath) { c = env->GetObjectClass(vw); printf(“start\n”); jobjectArray ret = (jobjectArray) env->NewObjectArray(100, c, vw);for (int i = 0; i < 100; i++) {jmethodID visualWordConstructor = env->GetMethodID(
• 
  cayrodev
  java android surfaceview
  Hi i have one application on google play countdown numbers and letters. in this application i have activitys. google sigin, archivements, and admob service. and i use google analitics, and ACRA for error reporting, i don’t use GLsurfaceView, but acra one time or two times a day send me this error:java.lang.RuntimeException: createWindowSurface failed EGL_BAD_ALLOC at android.view.HardwareRenderer$GlRenderer.createSurface(HardwareRenderer.java:763) at android.view.HardwareRenderer$GlRenderer.crea
• 
  RobV
  tomcat java servlets
  I have a Java web app which I’m deploying using Tomcat but I’m having some trouble with this.The problem is that my web app has to talk to some native libraries (via JNI) and those libraries do not handle errors that gracefully so if I try to start Tomcat and the native calls fail Tomcat startup halts partway through and does not start.What I would like to do is have Tomcat not start this web app when it starts as I’ll be using other means to start the web app which will ensure that the native c
• 
  quanta
  windows java socket
  I’m trying to diagnose why a Java-based app runs for a while as a client making SOAP webservice calls, and then starts hitting an exception whereby it cannot open a socket. The OS is Windows 2003 server SP1.The netstat -an output shows some connections in CLOSE_WAIT or TIME_WAIT, but not enough to suggest that the OS itself is out of sockets. I suspect that there’s an error in the way that the client-side API is being used (Axis2 v1.4), such that it fails to recycle some internal resource. Once
• 
  home
  java tomcat shared-libraries
  How do I load a shared library in Tomcat6, on Ubuntu?I have created a library “awragrids” with name “libawragrids.so” and placed it in/var/lib/tomcat6/sharedI have set the following environment variables in the terminal from which I call start tomcat:export PATH=$PATH:/var/lib/tomcat6/shared export JAVA_OPTS=”-Djava.library.path=/var/lib/tomcat6/shared” export LD_LIBRARY_PATH=/var/lib/tomcat6/sharedI then try and load the library withprivate static final String GRIDTOOL_LIBRARY_NAME = “awratools
• 
  mfinni
  windows-server-2008-r2 java
  We have a web proxy running as a service. It’s a straight-up EXE, within it is a packaged java application. Sometimes, we get this in the log file the application generates, and the proxy stops working.26-11-2013 09:42:48,661 [ServerThread] ERROR pe – Unable to start serverjava.net.SocketException: Unrecognized Windows Sockets error: 0: JVM_Bindat java.net.PlainSocketImpl.socketBind(Native Method)at java.net.PlainSocketImpl.bind(PlainSocketImpl.java:365)at java.net.ServerSocket.bind(ServerSocket
• 
  mark
  ubuntu networking java
  Please, observe:markk@ip-10-203-82-54:~/work/gl$ uname -a Linux ip-10-203-82-54 3.2.0-25-virtual #40-Ubuntu SMP Wed May 23 22:20:17 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux markk@ip-10-203-82-54:~/work/gl$ ls -la /etc/authbind/byport/80 -rwxrwx— 1 markk markk 0 Aug 16 10:00 /etc/authbind/byport/80 markk@ip-10-203-82-54:~/work/gl$ authbind /usr/bin/java -Dcom.shunra.gl.ports=80 -jar server.jar java.net.SocketException: Permission deniedat sun.nio.ch.Net.bind(Native Method)at sun.nio.ch.ServerSoc
• 
  Alpha Hydrae
  api rest inheritance polymorphism
  I have an object hierarchy I need to expose through a RESTful API and I’m not sure how my URLs should be structured and what they should return. I could not find any best practices.Let’s say I have Dogs and Cats inheriting from Animals. I need CRUD operations on dogs and cats; I also want to be able to do operations on animals in general.My first idea was to do something like this:GET /animals # get all animals POST /animals # create a dog or cat GET /animals/123 # get animal 123
• 
  Pooya
  ruby-on-rails ruby mongodb polymorphism polymorphic-associations
  my child model:include Mongoid::Documentinclude Mongoid::Timestampsbelongs_to :dedicated_to, polymorphic: true , touch: truemy parent model:include Mongoid::Document include Mongoid::Timestamps has_many :dedications, as: :dedicated_toand now see this:irb(main):050:0> Parent.find(“523aab9f8c1ec39417000242”).dedications.first.touch => true irb(main):050:0> a = Parent.find(“523aab9f8c1ec39417000242”).dedications.first.dedicated_to irb(main):050:0> b = Parent.find(“523aab9f8c1ec394170002
• 
  myahya
  c++ polymorphism
  Let’s say I have the following class hierarchy in C++:class Base; class Derived1 : public Base; class Derived2 : public Base;class ParamType; class DerivedParamType1 : public ParamType; class DerivedParamType2 : public ParamType;And I want a polymorphic function, func(ParamType), defined in Base to take a parameter of type DerivedParamType1 for Derived1 and a parameter of type DerivedParamType2 for Derived2.How would this be done without pointers, if possible?
• 
  Chris
  java polymorphism jackson deserialization
  I would like to know if @JsonTypeInfo annotation can be used for interfaces. I have set of classes which should be serialized and deserialized.Here is what I’m trying to do. I have two implementation classes Sub1, Sub2 implementing MyInt. Some of the model classes have the interface reference for the implementation types. I would like to deserialize the objects based on polymorphism@JsonTypeInfo(use=JsonTypeInfo.Id.NAME, include=As.WRAPPER_OBJECT) @JsonSubTypes({@Type(value=Sub1.class, value=”su
• 
  WhozCraig
  c++ oop vector polymorphism
  I have a tricky situation. Its simplified form is something like thisclass Instruction { public:virtual void execute() { } };class Add: public Instruction { private:int a;int b;int c; public:Add(int x, int y, int z) {a=x;b=y;c=z;}void execute() { a = b + c; } };And then in one class I do something like…void some_method() {vector<Instruction> v;Instruction* i = new Add(1,2,3)v.push_back(*i); }And in yet another class…void some_other_method() {Instruction ins = v.back();ins.execute();
• 
  meriton
  java inheritance compiler polymorphism
  Recently came across an interesting feature, which, though, can result in a unexpected output of Eclipse “add unimplemented methods” feature. What is the “googl-able” name of the language concept behind this “occasional implicit implementation”?I wouldn’t expect the code below to compile but it did and is workinginterface CallmeIfc {public void callme(); }class CallmeCode {public void callme() {// implementation } }class CallmeImpl extends CallmeCode implements CallmeIfc {// empty class body }p
• 
  Buhake Sindi
  java polymorphism overriding
  Polymorphism allows the programmer either to inherit, override or to overload an instance method of Parent Class. But, it won’t allow to make an instance method of parent class as more restrictive in child class. i.e it wont allow to use same name of parent class instance method, to declare as private in the child class.Also JVM identifies the parent class version of an instance method, if child class didn’t override it.Similarly why don’t JVM identifies the parent class version of an instance m
• 
  Josip Dorvak
  c++ polymorphism pure-virtual
  I have a class called course. Course has a pointer to a base class called Assessment.class Course{char* courseName;float fee;public:Assessment* assessment;Course();Course(Course&);Course(char*, float, Assessment *);~Course();friend ostream& operator <<(ostream& os, Course&); };Strickly for testing purposes, in the constructor i’m assigning the Assessment pointer to an ExamAssessment(a sub-class)Course::Course(){courseName = “something”;fee = 0;assessment = &ExamAssessme
• 
  Smith
  c++ class polymorphism virtual
  In my code, I have used three classes. See the implementation below:class Medicine { int a; }class Pain:public Medicine {int b; }class Comb:public Pain {string salt,com; }All classes have just parameterized constructors. And call() is likecall() {cout<<“You are in class the_name_of_the_class”<<endl; }I have defined a function with same name, call(), in all of them. (They are not declared as virtual till now)The code goes like:int main() { Pain *p[2];p[0]= new Comb(“Salt”,”
• 
  user1032752
  ruby-on-rails ruby polymorphism associations sti
  Can’t figure out why this would be happening:class Foo < ActiveRecord::Basebelongs_to :belongable, :polymorphic => truedef after_save if belongable.kind_of?(User)send(:some_method)endend endclass Bar < Foodef some_method#Do somethingend endclass Group < ActiveRecord::Basehas_many :belongings, :as => :belongable endclass User < ActiveRecord::Basehas_many :belongings, :as => :belongable endThe class ‘Bar’ is an STI model that inherits from Foo (Foo has a ‘type’ attr). Both Gro
• 
  Susei
  java inheritance super
  First off I’ll show you my code: public class Person { String _name; int _age; public Person(String name, int age){_name = name;_age = age; } public String toString(){return “Age:” + _age + “. Name: ” + _name;} }public class Principal extends Person{ String _gender; int _rank; public Principal(String name, int age, String gender, int rank){super(name, age);_gender = gender;_rank = rank; } public String toString(){return “Age:” + _age + ” .Name: ” + _name + ” .Gender: ” + _gender + ” .Rank: ” + _
• 
  Jibin
  python derived-class super base-class
  class baseClass():def __init__(self,mark,name):self.mark = markself.name = nameclass derivedClass(baseClass):b1 = derivedClass(name=’Jibin’) print b1.nameThis was my code initially & it worked fine.(Note: I don’t have access to baseClass)But later I had to pass a additional attribute rank to derivedClass.So I edited the code like this.class baseClass():def __init__(self,mark,name):self.mark = markself.name = nameclass derivedClass(baseClass):def __init__(self,rank):self.rank = rank b1 = deri
• 
  Lee
  ruby-on-rails activerecord inheritance super destroy
  I have a Commentable class that inherits from ActiveRecord::Base and an Event class that inherits from Commentables.I have overwritten the destroy methods in both of these classes, and Event.distroy calls super. However, some unexpected things happen. Specifically, the Event’s has_and_belongs_to_many associations are deleted. I think this is happening because some modules are getting included between the Commentables and the Event class, but not sure if there is a way to stop this.Here’s the sim
• 
  thefourtheye
  python class super
  I see everywhere examples that super-class methods should be called by:super(SuperClass, instance).method(args)Is there any disadvantage to doing:SuperClass.method(instance, args)
• 
  pvgoddijn
  java generics super return-type
  we have a method more or less like the following. however we currently return List which in function bla() would return List<Bar> at runtime.I’m looking for a way to make bothList<Interface> = troubleFuction(foo, bar.getCLass());;andList<Bar> = troubleFuction(foo, bar.getCLass());;possible. basicaly i want it to return List which would be compatible with interface however this gives the following error*Type mismatch: cannot convert from List<capture#3-of ? extends Bar> t
• 
  Yuri Romanchenko
  objective-c super
  I’ve read apple ‘messaging’ chapter from programming with objective – c and got several questions about self and super. AFAIK when compiler finds any message it translates it into objc_msgSend with two hidden parameters – receiver, selector and variable arguments for selector. for example [self test] will be something like that:objc_msgSend(self, @selector(test));if there is no method implementation in receiver’s dispatch table then function will try to find implementation in superclasses. supe
• 
  Krishnan
  objective-c self super
  I am new to Objective C.I am trying aout some example programs.I could not understand how the self and super methods work in objective C. In the pgm below CashTransaction.m [super trackSpending:amount] is called and in CreditCardTransaction.m [self trackSpending:amount] is called.I could not find difference between the self and super.super is for invoking the base class overriden method.and self is for invoking the child class overridden method.This is what my understanding is.please correct me
• 
  AedonEtLIRA
  java polymorphism super
  I have an init method that is used and overridden through out an extensive heirarchy. Each init call however extends on the work that the previous did. So naturally, I would:@Override public void init() {super.init(); }And naturally this would ensure that everything is called and instantiated. What I’m wondering is: Can I create a way to ensure that the super method was called? If all of the init’s are not call, there is a break down in the obejct, so I want to throw an exception or an error if
• 
  Michael Matheus
  cocoa subclass super
  Sorry if this is a repost but I couldn’t quite search for it because I can’t explain it in a few words. I have a super class with lots of methods but they will always (not all of them) be subclassed. From the super I need to run those methods. I could either leave the methods in super empty or I could just not type them in super but call them anyway like so [self myMethod] and it will call my subclassed method even if it doesn’t exist in super. This works but Xcode gives me an error though. ‘sup
• 
  Brad Parks
  objective-c category categories super
  I’d like to override a method in an Objective C class that I don’t have the source to.I’ve looked into it, and it appears that Categories should allow me to do this, but I’d like to use the result of the old method in my new method, using super to get the old methods result.Whenever I try this though, my method gets called, but “super” is nil… Any idea why? I’m doing iPhone development with the XCode 2.2 SDK. I’m definitely working with an instance of a class, and the method of the class is an

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