Almost. I’d write it like this: public class Pair<F, S> { private F first; //first member of pair private S second; //second member of pair public Pair(F first, S second) { this.first = first; this.second = second; } public void setFirst(F first) { this.first = first; } public void setSecond(S second) { this.second = second; … Read more
It’s because you can’t create, but you can use them: public class GenericsTest { //statement 1 public ArrayList<Integer>[] lists; public GenericsTest() { //statement 2 lists = new ArrayList[4]; //statement 3 lists[0].add(new Integer(0)); //statement 4 lists[0].add(new String(“”)); } } Statement 3 is possible, statement 4 will lead to a compiler error.
I think Miles Sabin solution is way too complex. Scala’s collection already have the necessary machinery to make it work, with a very small change: import scala.collection.TraversableLike def multiMinBy[A, B: Ordering, C <: Traversable[A]] (xs: C with TraversableLike[A, C]) (f: A => B): C = { val minVal = f(xs minBy f) xs filter (f(_) … Read more
Create a modelbinder, override BindModel, check the type and do what you need to do public class MyModelBinder : DefaultModelBinder { public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) { if (HasGenericTypeBase(bindingContext.ModelType, typeof(MyType<>)) { // do your thing } return base.BindModel(controllerContext, bindingContext); } } Set your model binder to the default in the global.asax protected void … Read more
Circular generic references are indeed possible. Java Generics and Collections includes several examples. For your case, such a specimen would look like this: public interface P2PNetwork<N extends P2PNetwork<N, C>, C extends P2PClient<N, C>> { void addClient(C client); } public interface P2PClient<N extends P2PNetwork<N, C>, C extends P2PClient<N, C>> { void setNetwork(N network); } class TorrentNetwork … Read more
why the compiler can’t retain the assignment safe? It knows that,by executing for instance, the method with an Integer List, it gets from i.get an Integer value. So it try to set an Integer value at index 0 to the same Integer list (i). Put differently, why does the compiler not know that the two … Read more
You could actually shorten it down considerably. You can think of the Select() extension method as a type converter. The conversion could then be written as this: List<Cards> target = dt.AsEnumerable() .Select(row => new Cards { // assuming column 0’s type is Nullable<long> CardID = row.Field<long?>(0).GetValueOrDefault(), CardName = String.IsNullOrEmpty(row.Field<string>(1)) ? “not found” : row.Field<string>(1), }).ToList();
Anyway, the problem is that I can’t really return just a single object from next(), and I also can’t have a Iterator take more than one type. So, any thoughts? Obviously you are going to need a light-weight “pair” class. This is roughly analogous to the Map.Entry inner class. Here’s a rough cut at a … Read more
An unbound type can be useful when your method doesn’t really care about the actual type. A primitive example would be this: public void printStuff(Iterable<?> stuff) { for (Object item : stuff) { System.out.println(item); } } Since PrintStream.println() can handle all reference types (by calling toString()), we don’t care what the actual content of that … Read more
I am just going to answer the differences between declaration-site and use-site variance, since, while C# and Java generics differ in many other ways, those differences are mostly orthogonal to variance. First off, if I remember correctly use-site variance is strictly more powerful than declaration-site variance (although at the cost of concision), or at least … Read more