Java nested wildcard generic won't compile

Question

I have a problem with bounded nested wildcards in Java generics.

Here\'s a common case:

public void doSomething(Set set) {}
         


        

Answer 1

So the problem is, doSomething could be implemented as:

public void doSomething(Map<String, Set<? extends Number>> map) {
    Set<Float> set = ...;
    map.put("xyz", set);
}

You need to decide what you actually mean.

Probably something like:

public void doSomething(Map<String, ? extends Set<? extends Number>> map) {}

Answer 2

this will work for you:

public void doSomething(Map<String, ? extends Set<? extends Number>> map) {}

Answer 3

To make code to work Create HashMap as:

Map<String, Set<? extents Number>> map = new HashMap<String, Set<? extents Number>>();