Generate all permutations of Java List. Uses Java 11 var.

GeneratePermutations.java

public class GeneratePermutations {
    static <E> List<E> addToCopy(List<E> original, int pos, E e) {
        final var r = new ArrayList<>(original);
        r.add(pos, e);
        return r;
    }
    
    public static <E> List<List<E>> generatePermutations(List<E> original) {
        if (original.isEmpty()) {
            return List.of(new ArrayList<>());
        }
        final int size = original.size();
        return generatePermutations(original.subList(1, size)).stream().flatMap(
                s -> IntStream.range(0, size).mapToObj(i -> addToCopy(s, i, original.get(0)))
        ).collect(Collectors.toList());
    }
}