Java Challenge - Balanced Binary Search Tree

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I had some trouble getting this challenge to run (and I had to create an internal TreeNode class to avoid errors). TreeNode has a constructor that takes in an Integer and makes it the .value
I used array slicing this time, and I made a function to do the slicing.

Here’s my code:

import java.lang.*;
import java.util.Arrays;

public class BalancedBST {

  public static Integer[] slice(Integer[] arr, int start, int afterEnd) {
    int length = afterEnd - start;
    Integer[] part = new Integer[length];
    int j = 0;
    for (int i = start; i < afterEnd; i++) {
      part[j] = arr[i];
      j++;
    }
    return part;
  }

  public static TreeNode balancedBst(Integer[] a) {
    if ((a == null) || (a.length < 1)) {
      return null;
    }
    else if (a.length == 1) {
      return new TreeNode(a[0]);
    }
    else {
      int mid = a.length / 2;  // integer division
      TreeNode node = new TreeNode(a[mid]);
      node.left = balancedBst(slice(a, 0, mid));
      node.right = balancedBst(slice(a, mid + 1, a.length));
      return node;
    }
  }
    
  public static void main(String[] args){
    Integer[] a = {1,2,3,4,5,6,7,8};
    TreeNode balancedTree = balancedBst(a);
    balancedTree.print();
  }
  /*
  public static class TreeNode {
    public Integer value;
    public TreeNode left; // initialized to null
    public TreeNode right; // initialized to null

    public TreeNode() {
      this.value = null;
    }
    public TreeNode(Integer value) {
      this.value = value;
    }
    public void print() {
      System.out.print(this.value);
      if (!(this.left == null && this.right == null)) {
        System.out.print(" -> ");
        if (this.left != null) {
          System.out.print(this.left.value);
          if (this.right != null) {
            System.out.print(",");
          }
        }
        if (this.right != null) {
          System.out.print(this.right.value);
        }
        System.out.println();
        if (this.left != null) {
          this.left.print();
        }
        if (this.right != null) {
          this.right.print();
        }
      }
      else {
        System.out.println();
      }
    }
  }
  */
}
version without slicing
  public static TreeNode balancedBst(Integer[] a, int start, int afterEnd) {
    if ((a == null) || start >= afterEnd) {
      return null;
    }
    else if ((start + 1) == afterEnd) {
      return new TreeNode(a[start]);
    }
    else {
      int mid = (start + afterEnd) / 2;  // integer division
      TreeNode node = new TreeNode(a[mid]);
      node.left = balancedBst(a, start, mid);
      node.right = balancedBst(a, mid + 1, afterEnd);
      return node;
    }
  }
  public static TreeNode balancedBst(Integer[] a) {
    return balancedBst(a, 0, a.length);
  }