Templating on values

Question

In C++ I can write code something like:
template <int N>
    class Array
        int array[N];
void main()
    Array<3> array3D; // etc
}Is this possible in Java?
John

Answer 1

"new E" is not allowed because the compiler has no way to know
if "E" has a noargs constructor. "new E[]" is not allowed
because the compiler doesn't have enough information to actually
allocate an array of the correct type.The error message in "new E" is correct. The syntax productions do not allow TypeVariable in a new expression.
The error message regarding "new E[]" must be a compiler error, I would think. Type variables are expressly allowed in array creation expressions according to the spec. Section 5.3. says:
"The element type in a an array creation expression is a fully parameterized type. Creating an array whose element type is a type variable generates an "unchecked" warning at compile-time."
In addition, section 2.3 allows arrays of wildcard parameterized types:
"Wildcard parameterized types may be used as component types of arrays."
Given the current specification of Java Generics, how can the compiler reject the following declarations:
package generics;
import java.util.*;
public class Arrays2<T> {
          private T[] arr = new T[0];
          private List<Integer>[] l1 = new ArrayList<Integer>[0];
          private ArrayList<? super Integer>[] l2 = new ArrayList<? super Integer>[0];
          private ArrayList<? extends Number>[] l3 = new ArrayList<? extends Number>[0];
          private List<?>[] l4 = new List<?>[0];
          private List[] l5 = new List[0];
}The compiler is truly unhappy with all these declarations, except the array of raw type:
Arrays2.java:7: arrays of generic types are not allowed
          private List<Integer>[] l1 = new ArrayList<Integer>[0];
                                     ^
Arrays2.java:8: arrays of generic types are not allowed
          private ArrayList<? super Integer>[] l2 = new ArrayList<? super Integer>[0];
                                                  ^
Arrays2.java:9: arrays of generic types are not allowed
          private ArrayList<? extends Number>[] l3 = new ArrayList<? extends Number>[0];
                                                   ^
Arrays2.java:10: arrays of generic types are not allowed
          private List<?>[] l4 = new List<?>[0];
                               ^
Arrays2.java:6: generic array creation
          private T[] arr = new T[0];
                                  ^
Arrays2.java:7: arrays of generic types are not allowed
          private List<Integer>[] l1 = new ArrayList<Integer>[0];
                                             ^
Arrays2.java:8: arrays of generic types are not allowed
          private ArrayList<? super Integer>[] l2 = new ArrayList<? super Integer>[0];
                                                          ^
Arrays2.java:9: arrays of generic types are not allowed
          private ArrayList<? extends Number>[] l3 = new ArrayList<? extends Number>[0];
                                                           ^
Arrays2.java:10: arrays of generic types are not allowed
          private List<?>[] l4 = new List<?>[0];
                                       ^
9 errorsAm I seeing compiler bugs in all these cases? Or am I seeing specification errors?