Merge Sort implementation in Java

MergeSorter.java

package jono.sorting;

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

public class MergeSorter {
  public static void main(String[] args) {
    MergeSorter sorter = new MergeSorter();

    int[] array = Stream.of(args[0].split(",")).mapToInt(Integer::parseInt).toArray();

    sorter.sort(array, new int [array.length], 0, array.length - 1);
    System.out.println(Arrays.toString(array));
  }

  public void sort(int[] numbers, int[] temp, int start, int end) {
    int[] left, right;
    int middle;

    if (start >= end) {
      return;
    }


    middle = (start + end) / 2;

    sort(numbers, temp, start, middle);
    sort(numbers, temp, middle + 1, end);

    merge(numbers, temp, start, end);
  }

  public void merge(int[] numbers, int[] temp, int leftStart,  int rightEnd) {
    int leftIndex, rightIndex, leftNum, rightNum, middle, leftEnd, rightStart, size, insertIndex;

    leftEnd = (leftStart + rightEnd) / 2;
    rightStart = leftEnd + 1;
    size = rightEnd - leftStart + 1;

    leftIndex = leftStart;
    rightIndex = rightStart;
    insertIndex = leftStart;

    while (leftIndex <= leftEnd && rightIndex <= rightEnd) {
      leftNum = numbers[leftIndex];
      rightNum = numbers[rightIndex];

      if (leftNum < rightNum) {
        temp[insertIndex] = leftNum;
        leftIndex += 1;
      } else {
        temp[insertIndex] = rightNum;
        rightIndex += 1;
      }

      insertIndex += 1;
    }

    System.arraycopy(numbers, leftIndex, temp, insertIndex, leftEnd - leftIndex + 1);
    System.arraycopy(numbers, rightIndex, temp, insertIndex, rightEnd - rightIndex + 1);
    System.arraycopy(temp, leftStart, numbers, leftStart, size);
  }
}

> javac MergeSorter.java
> java jono.sorting.MergeSorter 6,3,2,0,-1
=> [-1, 0, 2, 3, 6]