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javaobjectcastinginteger

How to convert a list of object to a list of integer in Java?

I have a inner list of object into a list and I want to convert it in a list of Integer, because I know that its elements are Integer.

List<List<Object>> valuesModel = FCSMs.get(0).getValues();
            for (List<Object> innerList : valuesModel) {

//CONVERT LIST OF OBJECT TO LIST OF INTEGER

}

How Can I do?

Solution

  • You can do it like this. Since you know that all objects are Integers, no checks are done to avoid ClassCastExceptions.

    • Stream the list of lists to a stream of lists.
    • Then flatten those lists into a stream of object.
    • cast the object to an Integer.
    • and collect into a List
    List<List<Object>> valuesModel = List.of(List.of(1,2,3,4), List.of(5,6,7,8));

List<Integer> integers = valuesModel.stream()
           .flatMap(Collection::stream)
            .map(ob->(Integer)ob)
             .collect(Collectors.toList());

System.out.println(integers);

    Prints

    [1, 2, 3, 4, 5, 6, 7, 8]