How to convert an ArrayList<Integer> to ArrayList<String>? [closed]

Question

I have to convert an Int arraylist to String Arraylist so JText in swing can print the numbers of the String ArrayList.

private static ArrayList<Integer> numen = new ArrayList<Integer>
((Collections.nCopies(49,0)));

private static ArrayList<String> numens = new ArrayList<String>
((Collections.nCopies(49, "0")));
for (int  myInt : numen){ numens.add(String.valueOf(myInt)); }

Answer 1

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
    
List<String> stringVals = numbers.stream().map(a -> a.toString()).collect(Collectors.toList());
stringVals.stream().forEach(System.out::println);

Answer 2

The code you are using for the conversion is fine:

ArrayList<String> numens = new ArrayList<String>();
for (int  myInt : numen) { 
    numens.add(String.valueOf(myInt)); 
}

As explained, in @Ryan's answer, you could also do this using Java 8+ streams. But (IMO) that is not a significant improvement.

Note: if you are looking for a way to do this without creating a new list, that is not possible in Java.

---

But the thing that puzzles me is your rationalization for doing this:

I have to convert an Integer Arraylist to String Arraylist so JText in Swing can print the numbers of the String ArrayList.

Firstly, there is no JText type. There is a JTextField or a JTextArea.

Secondly, neither of these class accept a List to populate the field or area.

So ...

If you are just populating a single field / area from a list, you are going to have to convert the list to a string. And if you are doing that, you don't need to convert an ArrayList<Integer> to an ArrayList<String> to do it. For example, just call toString() on the ArrayList<Integer> will format it so that it can be inserted into a JTextField or JTextArea.

If you are just populating a list or array of fields / areas from the list, you are going to have to iterate the list to do it. At that point, you may as well iterate the original ArrayList<Integer>.

In short, your question appears to be an XY problem.

Answer 3

toString

If your goal is a textual representation of the integers, just call AbstractCollection#toString on your original ArrayList< Integer >. No need to create another list.

List< Integer > integers = List.of( 1 , 2 , 3 ) ;
String output = integers.toString() ;

See this code run live at Ideone.com.

[1, 2, 3]

Stream#map

If your goal is generating text, use a stream to generate text with newlines. Calling Stream#map changes our stream of Integer objects into a stream of String objects. We combine those with a StringBuilder, producing a final multi-line String object at the end.

List < Integer > integers = List.of( 1 , 2 , 3 );
String s =
        integers
                .stream()
                .map( integer -> integer.toString() + "\n" )
                .collect( StringBuilder :: new , StringBuilder :: append , StringBuilder :: append )
                .toString();

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