[Well..]Merge Sort implementation

//Code from: https://www.cs.cmu.edu/~adamchik/15-121/lectures/Sorting%20Algorithms/code/MergeSort.java import java.util.*;

public class MergerSort
{
public static void main(String[] args)
{
Integer[] a = {2, 6, 3, 5, 1};
mergeSort(a);
System.out.println(Arrays.toString(a));
}

public static void mergeSort(Comparable [ ] a)
{
Comparable[] tmp = new Comparable[a.length];
mergeSort(a, tmp,  0,  a.length - 1);
}

private static void mergeSort(Comparable [ ] a, Comparable [ ] tmp, int left, int right)
{
if( left < right )
{
int center = (left + right) / 2;
mergeSort(a, tmp, left, center);
mergeSort(a, tmp, center + 1, right);
merge(a, tmp, left, center + 1, right);
}
}

private static void merge(Comparable[ ] a, Comparable[ ] tmp, int left, int right, int rightEnd )
{
int leftEnd = right - 1;
int k = left;
int num = rightEnd - left + 1;

while(left <= leftEnd && right <= rightEnd)
if(a[left].compareTo(a[right]) <= 0)
tmp[k++] = a[left++];
else
tmp[k++] = a[right++];

while(left <= leftEnd)    // Copy rest of first half
tmp[k++] = a[left++];

while(right <= rightEnd)  // Copy rest of right half
tmp[k++] = a[right++];

// Copy tmp back
for(int i = 0; i < num; i++, rightEnd--)
a[rightEnd] = tmp[rightEnd];
}
}