Recursive Merge Sort using Java 8

MergeSortRecursive.java

import java.util.Arrays;
import java.util.stream.Stream;

class MergeSortRecursive {
  
  public String[] sort(String[] items) {
    int length = items.length;
    if(length <= 1) return items;

    String[] left = sort(copy(items, 0, length/2));
    String[] right = sort(copy(items, length/2, length));
    return merge(left, right);
  }

  public String[] merge(String[] list1, String[] list2) {
    int lenList1 = list1.length;
    int lenList2 = list2.length;

    if(lenList1 <= 0) return list2;
    if(lenList2 <= 0) return list1;

    if(list1[0].compareTo(list2[0]) <= 0)
      return concatenate(list1[0], merge(copy(list1, 1, lenList1), list2));
    else
      return concatenate(list2[0], merge(list1, copy(list2, 1, lenList2)));
  }
  
  public final String[] concatenate(String list1, String[] list2) {
    return Stream.of(new String[]{list1}, list2)
            .flatMap(listArray -> Stream.of(listArray)).toArray(String[]::new);
  }
  
  public final String[] copy(String[] items, int start, int endExclusive) {
    return Arrays.copyOfRange(items, start, endExclusive);
  }
  
  public static void main(String[] args) {
    MergeSortRecursive mergesort = new MergeSortRecursive();
    String[] result = mergesort.sort(new String[]{"z", "a", "b", "t", "k", "m"});
    Stream.of(result).forEach(System.out::println);
  }
}