Question

Why this code comes out an error?

List<String>[] l = new ArrayList<String>[10];

Eclipse said I cannot create a generic array, but in fact I am trying to create a collection array.

Answer 1

Per the language spec, section 15.10:

"An array creation expression creates an object that is a new array whose elements are of the type specified by the PrimitiveType or ClassOrInterfaceType. It is a compile-time error if the ClassOrInterfaceType does not denote a reifiable type."

And per the language spec, section 4.7:

Because some type information is erased during compilation, not all types are available at run time. Types that are completely available at run-time are known as reifiable types.

A type is reifiable if and only if one of the following holds:

• It refers to a non-generic class or interface type declaration.

…

So put simply, "because the language says you can’t". I understand the ultimate cause dealt with maintaining backward compatibility, but I’m not familiar with the details.