Java：通用类型类型不匹配语法错误

Question

I have this declaration/initiation written for Java JDK 1.6

Map<String, <? extends List<?>>> groupThemTogether = new HashMap<String, ArrayList<String[]>>();

The error happens at the first comma. The error message is

Type mismatch: cannot convert from HashMap<String,ArrayList<String[]>> to Map<String,List>

Why doesn't this compile?

Answer 1

You've got too many angle brackets. Try this:

Map<String, ? extends List<?>> groupThemTogether = new HashMap<String, ArrayList<String[]>>();

This compiles for me.

Answer 2

Are you sure of this?

This, similar code, compiles OK for me:

Map<String, ? extends List<?>> groupThemTogether = new HashMap<String, ArrayList<String[]>>();