I have a `Map` like this:

```
Map<String, List<Integer>> numbersMap = new HashMap<>();
numbersMap.put("A", Arrays.asList(1,2,3));
numbersMap.put("B", Arrays.asList(4,5,6));
numbersMap.put("C", Arrays.asList(7,8, 9));

```

How do I get a `List` out of it?

```
List<Integer> allnumbers = //?

```

that contains `1, 2, 3, 4, 5, 6, 7, 8, 9` elements.