Converting nested lists using java streams

Is it possible to use streams to get the same results (as I currently get using the following nested for loop)?

List<String> people = Arrays.asList("John","Adam");
List<String> dogs = Arrays.asList("alex","rex");

List<List<String>> list = new ArrayList<List<String>>();
list.add(people);
list.add(dogs);

List<List<String>> list2 = new ArrayList<List<String>>();
for (int i = 0; i < list.size(); i++) {
    list2.add(new ArrayList<>());
    for (int j = 0; j < list.get(i).size(); j++) {
        list2.get(i).add(list.get(i).get(j).toUpperCase());
    }
}
System.out.println(list2);

I want this response:

[[JOHN,ADAM],[ALEX,REX]]

Use the following streams:

list. stream(). flatMap(l – > l.stream()). map(String :: toUpperCase). collect(Collectors.toList());

I can only get such things:

[JOHN,ADAM,ALEX,REX]

Solution

Flatmap doesn't help you because you don't want flat output You should convert each internal list to an uppercase list, and then collect all these lists into the final nested output list

List<List<String>> list2 = list.stream()
        .map(l -> l.stream().map(String::toUpperCase).collect(Collectors.toList()))
        .collect(Collectors.toList());

Output:

[[JOHN,REX]]