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• Interface and base class mix, the right way to implement this

  - by Lerxst

  I have some user controls which I want to specify properties and methods for. They inherit from a base class, because they all have properties such as "Foo" and "Bar", and the reason I used a base class is so that I dont have to manually implement all of these properties in each derived class. However, I want to have a method that is only in the derived classes, not in the base class, as the base class doesn't know how to "do" the method, so I am thinking of using an interface for this. If i put it in the base class, I have to define some body to return a value (which would be invalid), and always make sure that the overriding method is not calling the base. method Is the right way to go about this to use both the base class and an interface to expose the method? It seems very round-about, but every way i think about doing it seems wrong... Let me know if the question is not clear, it's probably a dumb question but I want to do this right.

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• Constructor ambiguous quesiton

  - by Crystal

  I'm trying to create a simple date class, but I get an error on my main file that says, "call of overloaded Date() is ambiguous." I'm not sure why since I thought as long as I had different parameters for my constructor, I was ok. Here is my code: header file: #ifndef DATE_H #define DATE_H using std::string; class Date { public: static const int monthsPerYear = 12; // num of months in a yr Date(int = 1, int = 1, int = 1900); // default constructor Date(); // uses system time to create object void print() const; // print date in month/day/year format ~Date(); // provided to confirm destruction order string getMonth(int month) const; // gets month in text format private: int month; // 1 - 12 int day; // 1 - 31 int year; // any year int checkDay(int) const; }; #endif .cpp file #include <iostream> #include <iomanip> #include <string> #include <ctime> #include "Date.h" using namespace std; Date::Date() { time_t seconds = time(NULL); struct tm* t = localtime(&seconds); month = t->tm_mon; day = t->tm_mday; year = t->tm_year; } Date::Date(int mn, int dy, int yr) { if (mn > 0 && mn <= monthsPerYear) month = mn; else { month = 1; // invalid month set to 1 cout << "Invalid month (" << mn << ") set to 1.\n"; } year = yr; // could validate yr day = checkDay(dy); // validate the day // output Date object to show when its constructor is called cout << "Date object constructor for date "; print(); cout << endl; } void Date::print() const { string str; cout << month << '/' << day << '/' << year << '\n'; // new code for HW2 cout << setfill('0') << setw(3) << day; // prints in ddd cout << " " << year << '\n'; // yyyy format str = getMonth(month); // prints in month (full word), day, year cout << str << " " << day << ", " << year << '\n'; } and my main.cpp #include <iostream> #include "Date.h" using std::cout; int main() { Date date1(4, 30, 1980); date1.print(); cout << '\n'; Date date2; date2.print(); }

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• How Can I Improve/SpeedUp This FrequentFunction in C?

  - by Peter Lee

  Hi folks, How can I improve / speed up this frequent function? #include <math.h> #include <stdio.h> #include <stdlib.h> #include <time.h> // Assumptions: x, y, z, a, b and c are all array of 10. // Requirement: return the value of ret; // get all elements of array c float fnFrequentFunction(const float* x, const float* y, const float* z, const float *a, const float *b, float *c, int M) { register float tmp; register float sum; register float ret = 0; int i; for (i = 0; i < M; i++) // M == 1, 2, 4, or 8 { sum = 0; tmp = x[0] - y[0]; sum += tmp * tmp * z[0]; tmp = x[1] - y[1]; sum += tmp * tmp * z[1]; tmp = x[2] - y[2]; sum += tmp * tmp * z[2]; tmp = x[3] - y[3]; sum += tmp * tmp * z[3]; tmp = x[4] - y[4]; sum += tmp * tmp * z[4]; tmp = x[5] - y[5]; sum += tmp * tmp * z[5]; tmp = x[6] - y[6]; sum += tmp * tmp * z[6]; tmp = x[7] - y[7]; sum += tmp * tmp * z[7]; tmp = x[8] - y[8]; sum += tmp * tmp * z[8]; tmp = x[9] - y[9]; sum += tmp * tmp * z[9]; ret += (c[i] = log(a[i] * b[i]) + sum); } return ret; } int main() { float x[10] = {0.001251f, 0.563585f, 0.193304f, 0.808741f, 0.585009f, 0.479873f, 0.350291f, 0.895962f, 0.622840f, 0.746605f}; float y[10] = {0.864406f, 0.709006f, 0.091433f, 0.995727f, 0.227180f, 0.902585f, 0.659047f, 0.865627f, 0.846767f, 0.514359f}; float z[10] = {0.866817f, 0.581347f, 0.175542f, 0.620197f, 0.781823f, 0.778588f, 0.938688f, 0.721610f, 0.940214f, 0.811353f}; float a[10] = {0.870205f, 0.733879f, 0.711386f, 0.588244f, 0.484176f, 0.852962f, 0.168126f, 0.684286f, 0.072573f, 0.632160f}; float b[10] = {0.871487f, 0.998108f, 0.798608f, 0.134831f, 0.576281f, 0.410779f, 0.402936f, 0.522935f, 0.623218f, 0.193030f}; float c[8]; int i; int n = 10000000; long start; // Speed test here: start = clock(); while(--n) fnFrequentFunction(x, y, z, a, b, c, 8); printf("Time used: %ld\n", clock() - start); printf("fnFrequentFunction == %f\n", fnFrequentFunction(x, y, z, a, b, c, 8)); for(i = 0; i < 8; ++i) printf(" c[%d] == %f\n", i, c[i]); printf("\n"); return 0; } Any suggestions are welcome :-)

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• Authorization in a more purely OOP style...

  - by noblethrasher

  I've never seen this done but I had an idea of doing authorization in a more purely OO way. For each method that requires authorization we associate a delegate. During initialization of the class we wire up the delegates so that they point to the appropriate method (based on the user's rights). For example: class User { private deleteMemberDelegate deleteMember; public StatusMessage DeleteMember(Member member) { if(deleteMember != null) { deleteMember(member); } } //other methods defined similarly... User(string name, string password) //cstor. { //wire up delegates based on user's rights. //Thus we handle authentication and authorization in the same method. } } This way the client code never has to explictly check whether or not a user is in a role, it just calls the method. Of course each method should return a status message so that we know if and why it failed. Thoughts?

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• Incorrect results for frustum cull

  - by DeadMG

  Previously, I had a problem with my frustum culling producing too optimistic results- that is, including many objects that were not in the view volume. Now I have refactored that code and produced a cull that should be accurate to the actual frustum, instead of an axis-aligned box approximation. The problem is that now it never returns anything to be in the view volume. As the mathematical support library I'm using does not provide plane support functions, I had to code much of this functionality myself, and I'm not really the mathematical type, so it's likely that I've made some silly error somewhere. As follows is the relevant code: class Plane { public: Plane() { r0 = Math::Vector(0,0,0); normal = Math::Vector(0,1,0); } Plane(Math::Vector p1, Math::Vector p2, Math::Vector p3) { r0 = p1; normal = Math::Cross((p2 - p1), (p3 - p1)); } Math::Vector r0; Math::Vector normal; }; This class represents one plane as a point and a normal vector. class Frustum { public: Frustum( const std::array<Math::Vector, 8>& points ) { planes[0] = Plane(points[0], points[1], points[2]); planes[1] = Plane(points[4], points[5], points[6]); planes[2] = Plane(points[0], points[1], points[4]); planes[3] = Plane(points[2], points[3], points[6]); planes[4] = Plane(points[0], points[2], points[4]); planes[5] = Plane(points[1], points[3], points[5]); } Plane planes[6]; }; The points are passed in order where (the inverse of) each bit of the index of each point indicates whether it's the left, top, and back of the frustum, respectively. As such, I just picked any three points where they all shared one bit in common to define the planes. My intersection test is as follows (based on this): bool Intersects(Math::AABB lhs, const Frustum& rhs) const { for(int i = 0; i < 6; i++) { Math::Vector pvertex = lhs.TopRightFurthest; Math::Vector nvertex = lhs.BottomLeftClosest; if (rhs.planes[i].normal.x <= -0.0f) { std::swap(pvertex.x, nvertex.x); } if (rhs.planes[i].normal.y <= -0.0f) { std::swap(pvertex.y, nvertex.y); } if (rhs.planes[i].normal.z <= -0.0f) { std::swap(pvertex.z, nvertex.z); } if (Math::Dot(rhs.planes[i].r0, nvertex) < 0.0f) { return false; } } return true; } Also of note is that because I'm using a left-handed co-ordinate system, I wrote my Cross function to return the negative of the formula given on Wikipedia. Any suggestions as to where I've made a mistake?

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• Inheritance classes in Scheme

  - by DreamWalker

  Now I research OOP-part of Scheme. I can define class in Scheme like this: (define (create-queue) (let ((mpty #t) (the-list '())) (define (enque value) (set! the-list (append the-list (list value))) (set! mpty #f) the-list) (define (deque) (set! the-list (cdr the-list)) (if (= (length the-list) 0) (set! mpty #t)) the-list) (define (isEmpty) mpty) (define (ptl) the-list) (define (dispatch method) (cond ((eq? method 'enque) enque) ((eq? method 'deque) deque) ((eq? method 'isEmpty) isEmpty) ((eq? method 'print) ptl))) dispatch)) (Example from css.freetonik.com) Can I implement class inheritance in Scheme?

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• Create a New .Net Profiler Api

  - by daniel

  Hi everybody! i m a new programmer in .Net Profiler and Visual C++, i read many forums and weblogs for .Net Profiling and i have this question. my Profiler application must be a unmanaged code or i can use some class in .Net in my application? and what type of project i must create ATL with MFC Or ..? another question is how can i register my profiler dll file that every application of my computer use this profiler? where the best situation for re-write IL of a method (Enter method of profiler or JITCompilationStarted)? how can i get input variables of old method and send to new method? how can i change IL of a property or whole of a class? i want chane all datetime format of my dlls, and i think that i must search name of those method in JITCompilationStarted and then rewrite that methods,Do u have any better solution? thanks alot.

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• php java in memory database

  - by msaif

  i need to load data as array to memory in PHP.but in PHP if i write $array= array("1","2"); in test.php then this $array variable is initialized every time user requests.if we request test.php 100 times by clicking 100 times browser refresh button then this $array variable will be executed 100 times. but i need to execute the $array variable only one time for first time request and subsequent request of test.php must not execute the $array variable.but only use that memory location.how can i do that in PHP. but in JAVA SEVRVLET it is easy to execute,just write the $array variable in one time execution of init() method of servlet lifecycle method and subsequent request of that servlet dont execute init() method but service() method but service() method always uses that $array memeory location. all i want to initilize $array variable once but use that memory loc from subsequent request in PHP.is there any possiblity in PHP?

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• Bullet Physics implementing custom MotionState class

  - by Arosboro

  I'm trying to make my engine's camera a kinematic rigid body that can collide into other rigid bodies. I've overridden the btMotionState class and implemented setKinematicPos which updates the motion state's tranform. I use the overridden class when creating my kinematic body, but the collision detection fails. I'm doing this for fun trying to add collision detection and physics to Sean O' Neil's Procedural Universe I referred to the bullet wiki on MotionStates for my CPhysicsMotionState class. If it helps I can add the code for the Planetary rigid bodies, but I didn't want to clutter the post. Here is my motion state class: class CPhysicsMotionState: public btMotionState { protected: // This is the transform with position and rotation of the camera CSRTTransform* m_srtTransform; btTransform m_btPos1; public: CPhysicsMotionState(const btTransform &initialpos, CSRTTransform* srtTransform) { m_srtTransform = srtTransform; m_btPos1 = initialpos; } virtual ~CPhysicsMotionState() { // TODO Auto-generated destructor stub } virtual void getWorldTransform(btTransform &worldTrans) const { worldTrans = m_btPos1; } void setKinematicPos(btQuaternion &rot, btVector3 &pos) { m_btPos1.setRotation(rot); m_btPos1.setOrigin(pos); } virtual void setWorldTransform(const btTransform &worldTrans) { btQuaternion rot = worldTrans.getRotation(); btVector3 pos = worldTrans.getOrigin(); m_srtTransform->m_qRotate = CQuaternion(rot.x(), rot.y(), rot.z(), rot.w()); m_srtTransform->SetPosition(CVector(pos.x(), pos.y(), pos.z())); m_btPos1 = worldTrans; } }; I add a rigid body for the camera: // Create rigid body for camera btCollisionShape* cameraShape = new btSphereShape(btScalar(5.0f)); btTransform startTransform; startTransform.setIdentity(); // forgot to add this line CVector vCamera = m_srtCamera.GetPosition(); startTransform.setOrigin(btVector3(vCamera.x, vCamera.y, vCamera.z)); m_msCamera = new CPhysicsMotionState(startTransform, &m_srtCamera); btScalar tMass(80.7f); bool isDynamic = (tMass != 0.f); btVector3 localInertia(0,0,0); if (isDynamic) cameraShape->calculateLocalInertia(tMass,localInertia); btRigidBody::btRigidBodyConstructionInfo rbInfo(tMass, m_msCamera, cameraShape, localInertia); m_rigidBody = new btRigidBody(rbInfo); m_rigidBody->setCollisionFlags(m_rigidBody->getCollisionFlags() | btCollisionObject::CF_KINEMATIC_OBJECT); m_rigidBody->setActivationState(DISABLE_DEACTIVATION); This is the code in Update() that runs each frame: CSRTTransform srtCamera = CCameraTask::GetPtr()->GetCamera(); Quaternion qRotate = srtCamera.m_qRotate; btQuaternion rot = btQuaternion(qRotate.x, qRotate.y, qRotate.z, qRotate.w); CVector vCamera = CCameraTask::GetPtr()->GetPosition(); btVector3 pos = btVector3(vCamera.x, vCamera.y, vCamera.z); CPhysicsMotionState* cameraMotionState = CCameraTask::GetPtr()->GetMotionState(); cameraMotionState->setKinematicPos(rot, pos);

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• Should functions of a C library always expect a string's length?

  - by Benjamin Kloster

  I'm currently working on a library written in C. Many functions of this library expect a string as char* or const char* in their arguments. I started out with those functions always expecting the string's length as a size_t so that null-termination wasn't required. However, when writing tests, this resulted in frequent use of strlen(), like so: const char* string = "Ugh, strlen is tedious"; libFunction(string, strlen(string)); Trusting the user to pass properly terminated strings would lead to less safe, but more concise and (in my opinion) readable code: libFunction("I hope there's a null-terminator there!"); So, what's the sensible practice here? Make the API more complicated to use, but force the user to think of their input, or document the requirement for a null-terminated string and trust the caller?

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• JavaScript: How to create a new instance of a class without using the new keyword?

  - by Alessandro Vernet

  I think the following code will make the question clear. // My class var Class = function() { console.log("Constructor"); }; Class.prototype = { method: function() { console.log("Method");} } // Creating an instance with new var object1 = new Class(); object1.method(); console.log("New returned", object1); // How to write a factory which can't use the new keyword? function factory(clazz) { // Assume this function can't see "Class", but only sees its parameter "clazz". return clazz.call(); // Calls the constructor, but no new object is created return clazz.new(); // Doesn't work because there is new() method }; var object2 = factory(Class); object2.method(); console.log("Factory returned", object2);

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• problems with extended classes and overwrite with methods

  - by Marco

  I have a .net website written in C# and will make functionalities that other developers can use. So i will make some default implementation and a developer can overwrite some methods Example: i have a class ShoppingCart and a class Product the class product haves a method getProductPrice the shoppingcart will call the method getProductPrice for calculating the total price of cart The Shoppingcart and Product are in the same project and i will give the developers the .dll so they can't change the source code so we can update the assembly later So they need to make a other project and extend the product class and overwrite the method getProductPrice so they can implement there own logic The problem is that the shoppingcart will not call the extended method but the original If we make already a extended project for the developers and the shoppingcart will call the extended method then we have a circular reference because the extended product needs a reference to product and the shopping cart to the extended product partial classes also don't works because we only can use partials within the same assembly anyone a suggestion ? thanks in advance

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• java methods and race condition in a jsp/servlets application.

  - by A.S al-shammari

  Hi. Suppose that I have a method called doSomething() and I want to use this method in a multithreaded application (each servlet inherits from HttpServlet).I'm wondering if it is possible that a race condition will occur in the following cases: doSomething() is not staic method and it writes values to a database. doSomething() is static method but it does not write values to a database. what I have noticed that many methods in my application may lead to a race condition or dirty read/write. for example , I have a Poll System , and for each voting operation, a certain method will change a single cell value for that poll as the following: [poll_id | poll_data ] [1 | {choice_1 : 10, choice_2 : 20}] will the JSP/Servlets app solve these issues by itself, or I have to solve all that by myself? Thanks..

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• Sending an email when an Exception is Thrown

  - by hariubc

  Hi: I have written a java class where if a method throws an exception, an email is sent, via java mail, with a report to the administrators. It works - my question is w.r.t elegance - to catch the exception thrown by the main method, the sendEmail() method resides in the catch block of the main method. The sendEmail() method has its own try-catch block. In effect - it looks like below - is there a more beautiful way of writing this? try { foo; } catch { try{ sendEmail(); } catch { log(e.message); } }

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• javascript inherance? with Private vars and methods too

  - by Totty

  Hy i need to inherent a class from another. Parent has private var "_data" and private method "_test" and public method "add" Now the child have a public method "add", that uses the private method from the parent "_test" and the private var "_data". How do i do this? var Parent = function(){ var _data = {}; var _test = function(){alert('test')}; this.add = function(){alert('add from parent')} } var Child = function(){ this.add = function(){// here uses the _data and _test from the Parent class alert('add from child') } } // something to inherent Child from Parent // instance Child and use the add method And i think im miss the prototype concept (http://stackoverflow.com/questions/892467/javascript-inheritance)

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• Are closures in javascript recompiled

  - by Discodancer

  Let's say we have this code (forget about prototypes for a moment): function A(){ var foo = 1; this.method = function(){ return foo; } } var a = new A(); is the inner function recompiled each time the function A is run? Or is it better (and why) to do it like this: function method = function(){ return this.foo; } function A(){ this.foo = 1; this.method = method; } var a = new A(); Or are the javascript engines smart enough not to create a new 'method' function every time? Specifically Google's v8 and node.js. Also, any general recommendations on when to use which technique are welcome. In my specific example, it really suits me to use the first example, but I know thath the outer function will be instantiated many times.

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• Java reflection for generics

  - by Vijay Bhore

  I am using Java Reflection to expose methods in custom eclipse tool. I am writing method getReturnType which accepts java.lang.reflect.Method as input and returns object of Class private static Class<?> getReturnType(Method method) { Type type = ((ParameterizedType)method.getGenericReturnType()).getRawType(); return getClass(type); } This code compiles well but at runtime i get the below exception while casting Type to ParameterizedType. java.lang.ClassCastException: java.lang.Class cannot be cast to java.lang.reflect.ParameterizedType Please suggest. Thanks!

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• Java generics question

  - by user247866

  So I have 3 classes. Abstract class A Class B extends class A independent Class C In class D that contains the main method, I create a list of instances of class B List<B> b = methodCall(); // the method returns a list of instances of class B Now in class C I have one method that is common to both A and B, and hence I don't want to duplicate it. I want to have one method that takes as input an instance of class A, as follows: public void someMethod(List<A> a) However, when I do: C c = new C(); c.someMethod(b); I get an error that some-method is not applicable for the argument List<B>, instead it's expecting to get List<A>. Is there a good way to fix this problem? Many thanks!

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• Why is run() not immediately called when start() called on a thread object in java

  - by pi

  Or is it? I have a thread object from: Thread myThread = new Thread(pObject); Where pObject is an object of a class implementing the Runnable interface and then I have the start method called on the thread object like so: myThread.start(); Now, my understanding is that when start() is called, the JVM implicitly (and immediately) calls the run() method which may be overridden (as it is in my case) However, in my case, it appears that the start() method is not called immediately (as desired) but until the other statements/methods are completed from the calling block i.e. if I had a method after the start() call like so: myThread.start(); doSomethingElse(); doSomthingElse() gets executed before the run() method is run at all. Perhaps I am wrong with the initial premise that run() is always called right after the start() is called. Please help! The desired again is making executing run() right after start(). Thanks.

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• NSMutableSet addObject question

  - by Jacob Relkin

  I've got a class that wraps around an NSMutableSet object, and I have an instance method that adds objects (using the addObject: method) to the NSMutableSet. This works well, but I'm smelling a performance hitch because inside the method i'm explicitly calling containsObject: before adding the object to the set. Three part question: Do I need to be calling containsObject: before I add an object to the set? If so, then what actual method should I be using, containsObject or containsObjectIdenticalTo:? If that is not so, what contains method gets invoked under the hood of addObject:? This is important to me because if I pass an object to containsObject: it would return true, but if I pass it to containsObjectIdenticalTo: it would return false.

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• Address calling class

  - by Samuel

  I have an abstract class Moveable with the method abstract void move() which is extended by the class Bullet and the abstract class Character, and Character is extended by the class Survivor and the class Zombie. In Survivor and Bullet the move() method doesnt require any parameters while in the class Zombie the move() method depends on the actual position of the survivor. The survivor and multiple zombies are created in the class Gui. I wanted to access the survivor in Zombie - what's the best way of doing this? In Gui i wrote a method getSurvivor() but i don't see how to access this method in Zombie? I am aware that as a workaround i could just pass a [Survivor survivor] as parameter in move() and ignore it in Bullet and Survivor, but that feels so ... bad practice.

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• How to get back to auto-completion after misspelling of a methodname in Eclipse?

  - by Jonas

  When I am coding Java in Eclipse I like the auto-completion feature. With that I mean the popup with method-names that comes when you start typing in a method name for an object. Or maybe it's called something different, i.e. method-suggestions? But the popup is hidden if I misspells a method name, and it doesn't come back if I delete the misspelled part of the method name. Is there any way to get back the popup after a misspelling without starting to type in the hole methodname again?

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• Reflection & Parameters in C#

  - by Jim

  Hello, I'm writing an application that runs "things" to a schedule. Idea being that the database contains assembly, method information and also the parameter values. The timer will come along, reflect the method to be run, add the parameters and then execute the method. Everything is fine except for the parameters. So, lets say the method accepts an ENUM of CustomerType where CustomerType has two values of CustomerType.Master and CustomerType.Associate. EDIT I don't the type of parameter that will be getting passed in. ENUM used as an example END OF EDIT We want to run Method "X" and pass in parameter "CustomerType.Master". In the database, there will be a varchar entry of "CustomerType.Master". How do I convert the string "CustomerType.Master" into a type of CustomerType with a value of "Master" generically? Thanks in advance, Jim

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• Do I need the 'w' component in my Vector class?

  - by bobobobo

  Assume you're writing matrix code that handles rotation, translation etc for 3d space. Now the transformation matrices have to be 4x4 to fit the translation component in. However, you don't actually need to store a w component in the vector do you? Even in perspective division, you can simply compute and store w outside of the vector, and perspective divide before returning from the method. For example: // post multiply vec2=matrix*vector Vector operator*( const Matrix & a, const Vector& v ) { Vector r ; // do matrix mult r.x = a._11*v.x + a._12*v.y ... real w = a._41*v.x + a._42*v.y ... // perspective divide r /= w ; return r ; } Is there a point in storing w in the Vector class?

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• how to specify which child class this object belong to after retrieving from a hashmap?

  - by chandra wibowo

  hi everyone, i have a parent class called Course, and two child class PostgradCourse and UndergradCourse. i have a hashmap HashMap courses; i store all the postgradCourse and undergradCourse objects in the hashmap. i want to retrieve an undergradCourse object from the hashmap using the key. Course course = courses.get(courseCode); then i want to call a method in the UndergradCourse class, setUnits() method course.setUnits(); but the compiler say cannot find symbol- method setUnit() im pretty sure the problem is the compiler is looking for a method setUnit() in the Course class instead of UndergradCourse class i did this but its not working UndergradCourse course = courses.get(courseCode); results in incompatible type so how can i retrieve undergradCourse object from the hashmap as an undergradCourse object instead of course object? so then i can call a method inside the child class thanks in advance

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