instantiation

I was looking through my OOP class documentation and I found this example: class Student { private String name; public int averageGrade; public Student(String n, int avg) { name = n; averageGrade = avg; } public static void main(String[] args) { Student s = new Student("John", 9); } } I find it confusing that they are instantiating an object from the main of the same class. Is this considered bad practice? Will the newly created object s have a main method? Thank you! There's nothing wrong at all with this. It's entirely normal. (Admittedly it would make more sense for a class with a main

I would like to create an instance of a specified class using its name. My code is shown below. I get a compiler warning. Am I doing this the right way? Is it even possible to use the name of a class and get an instance of that type back, as I don't think there is any way of the compiler knowing what the type should be? public static <T> T create(final String className) { try { final Class<?> clazz = Class.forName(className); //WARNING: Type safety: Unchecked cast from capture#2-of ? to T return (T) create(clazz); } catch (ClassNotFoundException e) { e.printStackTrace(); } } public static <T>

I have a class and an interface, and when I try to instantiate the interface, I get an error: Cannot create an instance of the abstract class or interface My code is below: namespace MyNamespace { public interface IUser { int Property1 { get; set; } string Property2 { get; set; } string Property3 { get; set; } void GetUser(); } public class User : IUser { public int Property1 { get; set; } public string Property2 { get; set; } public string Property3 { get; set; } public void GetUser() { //some logic here...... } } } When I try to instantiate IUser user = new IUser(); I get an error: Cannot

Why are we not forced to instantiate a struct, like when using a class? The why is simply - because the spec says so . The how is a matter of ensuring that the entire block of memory is "definitely assigned", which means: assigning a value to each field of the struct. However, this requires 2 nasty things: public fields (almost always bad) mutable fields (generally bad in a struct) so in most best-practice cases , you do need to use the new(...) syntax, to invoke the constructor (or to zero-the memory, for the parameterless constructor) for the type correctly. Eric Lippert Why are we not

I am trying to make a screen capturing program. What I have is a transparent window, which will give the area to be captured, with a button capture on it, and I am trying to instantiate a class captureScreen that works good when captureScreen is individually executed using a command prompt I am trying to instantiate this captureScreen class when button capture is hit. I have tried keeping this class on my screenrecord.java , putting the code in event listener also. In both these cases,I get these errors AWTException,must be caught or declared in Robot robot = new Robot(); and IOException in

I just read the wiki article about CRTP , and I'm a little confused about template instantiation. According to the wiki, member function bodies (definitions) are not instantiated until long after their declarations. I don't quite understand what it means. Suppose I got a class template: template <typename T> class A { public: void foo(T t) { //... }; }; When I instantiate the class template A, does it instantiate the member function foo()? For example: //in .cpp file int main() { A<int> a; //question 1 //class template is instantiated here, isn't it? //What about foo(), is it instantiated too?

Does System.Activator.CreateInstance(T) method have performance issues (since I'm suspecting it uses reflection) big enough to discourage us from using it casually? As always, the only correct way to answer a question about performance is to actually measure the code. Here's a sample LINQPad program that tests: Activator.CreateInstance new T() calling a delegate that calls new T() As always, take the performance program with a grain of salt, there might be bugs here that skews the results. The output (timing values are in milliseconds): Test1 - Activator.CreateInstance<T>() 12342 Test2 - new T