How to initialize List/Map in a constructor?

Question

I know how to initialize other variables such as int or String in constructor but I have no clue how to do it for List and Map.

class StackOverFlowQuestion{
StackOverFlowQuestion({this.test='', this.map=?, this.list=?});
String test;
Map map;
List list;
}

What shall I replace the question marks with?

Thanks.