I read about Java's type erasure on Sun's website (http://java.sun.com/docs/books/tutorial/java/generics/erasure.html). I have the following question : When does type erasure occur - at compile time / runtime:when the class is loaded / runtime:when the class is instantiated. A lot of sites (including the Sun tutorial mentioned above) ...
Can someone explain to me why @Override public void fooMethod(Class<?> c) doesn't override public void fooMethod(Class c) and gives me the following errors instead: - Name clash: The method fooMethod(Class<?>) of type SubClass has the same erasure as fooMethod(Class) of type SuperClass but does not override it - The method f...
I may have designed myself into a corner with this problem but I feel like there's a workable known solution to something like this that I'm not seeing. It may well be that I'm completely overcomplicating the problem and skipped over the obvious solution. Any advice would be greatly appreciated. I have a set of entities defined as inter...
As I understand them, generics are a compile time feature of Java, and parametrized type information does not exist in the compiled byte code. I have now discovered the Field#getGenericType and Method#getGenericReturnType methods, thusly shattering my world view. Please help me to piece it together. ...
Suppose I have a class and I want to use it somewhere as a generic type: class MyList<T> { T[] list=T[10]; public void add(T element) { list[0]=element; } } After compilation, does it remove its type information like it is the case for generic collections? I don't need to use this code anywhere, so please do...
It's a sad fact of life on Scala that if you instantiate a List[Int], you can verify that your instance is a List, and you can verify that any individual element of it is an Int, but not that it is a List[Int], as can be easily verified: scala> List(1,2,3) match { | case l : List[String] => println("A list of strings?!") | cas...
Hello. I've made an example to demonstrate my problem: Metrical.java public interface Metrical<T> { double distance(T other); } Widget.java public class Widget implements Metrical<Widget> { private final double value; public Widget(double value) { this.value = value; } public double getValue() { return value; } ...
I would like to write a class looking like this: class Store[+A](dest: Symbol)(implicit c: String => A) extends Action(dest) { override def update(options: HashMap[Symbol,Any], arg: String): Unit = { options += ((dest -> c(arg))) } } object Store { def apply[A](dest: Symbol)(c: String=>A) = new Store[A](dest)(c) def apply[A...
There are lots of threads about this type of question, but I want to get a complete answer and actually understand it without 'hiding' the problem with a @SupressWarnings ! I have the following class (from a simple Spring tutorial) public class CarValidator implements Validator { public boolean supports(Class aClass) { return Car.cla...
I have a class like this : public class SubClass <T> extends SuperClass<Collection<T>>{ public Class<T> getInner() { // What goes here? } } Where SuperClass is simply a generic class. My question is how to gain access to a Class object in order to return it? I can't seem to be able to do this because of Type erasure. Any ...
So, the group I work with has reduced the amount of code we have to type for certain things. In this case, a Spring web page that displays a list using the DisplayTag libraries. The way it's done is with a class using generics extending the Controller object, and then a subclass of that for each page it should work on. This controller...
Suppose class B extends class A. I have a List<A> that I happen to know only contains instances of B. Is there a way I can cast the List<A> to a List<B>? It seems my only option is to iterate over the collection, casting one element at time, creating a new collection. This seems like an utter waste of resources given type erasure makes ...
Hi, I'm trying to create java to xsd for a java type that looks like this. public class MainRequest<E extends AParentType<Person>> extends EObject { private Transaction tran; private E e; private String email; } public class SubRequest extends MainRequest<AChildType> { } where AChildType extends AParentType. when i try to create a s...
There's a less common C++ idiom that I've used to good effect a few times in the past. I just can't seem to remember if it has a generally used name to describe it. It's somewhat related to mixins, CRTP and type-erasure, but is not specifically any of those things. The problem is found when you want to add some implementation to a clas...
I was writing something using generics and to my surprise I found that this doesn't work: class foo<T>{ T innerT = new T(); } So can't I instantiate the genericized type? Aren't there any ways to do this? ...
Hi scala gurus Can anyone re-write this code to do the same thing but without any compiler warnings please:- object TestTypeErasure { def main(args:Array[String]) { def myFunction(myObject:Any):Boolean = { true } val myVariable: (Any => Boolean) = myFunction myVariable match { case function:(Any => Boo...
I'm trying to bind an interface to its implementation as read from a configuration file so that I can feed it to my IoC container. Here's roughly what I'm trying to do: public class PropertyImplementationBinder<T> { // ... public Class getInterfaceClass() { return T.class; // OR Class<T>, note T is not newable } ...
Given the following code: public void example(Object o) { if(o instanceof List<MyType>) //do something } I understand that this is not possible (and why its not possible) given the way Java handles generics and type erasure. My question is, what is the best/cleanest way to accomplish this? Or is the only thing I can do is check...
My obviously wrong understanding of Java Generics was up to now, that Type Erasure removes all type information such that there is nothing left at all at runtime. Recently i stumbled upon a code fragment where i had to ask myself: How the hack does this work? Simplified it presents as import java.lang.reflect.ParameterizedType; import...
import java.lang.reflect.Array; public class PrimitiveArrayGeneric { static <T> T[] genericArrayNewInstance(Class<T> componentType) { return (T[]) Array.newInstance(componentType, 0); } public static void main(String args[]) { int[] intArray; Integer[] integerArray; intArray = (int[]) Array....