How to type-cast a nested Array of Objects into a nested List of Strings

Question

Cannot create nested ArrayList from Array in Java

I am trying to create a nested list from an array.

But I have a problem while converting Object to String:

Object[] array = new Object[] {
                    new String[] {"add, hack"},
                    new String[] {"add, hackerrank"},
                    new String[] {"find, hac"},
                    new String[] {"find, hak"}
};

List<List<String>> list = Arrays.asList(Arrays.asList((array.toString())));

So, how can I convert it properly?

Here is the method that reserves the List<List<String>>:

public static List<Integer> contacts(List<List<String>> queries) {
    for (List<String> query : queries) {
        String operation = query.get(0); // --> gives "add, hack" (I expect "add")
        String word = query.get(1);
    }
}

Answer 1

One more solution assuming you want to start from Object[] array - first transforms to list of String[] using casting and then maps every String[] to List:

    List<String[]> arrList = new ArrayList<>();

    for (Object o : array)
        arrList.add((String[]) o);

    List<List<String>> strList = arrList.stream()
            .map(Arrays::asList)
            .collect(Collectors.toList());