recursive merge sort in java, just for study

MergeSort.java

import java.util.Arrays;


public class MergeSort{

  public static void main(String[] args) {
		int a[]= { 5, 7, 2, 8, 11, 34, 2, 0, 7};
        System.out.println("Prima: "+Arrays.toString(a)+"\n");
        merge_sort(a);
        System.out.println("Dopo: "+Arrays.toString(a));
	}

	public static void merge_sort(int[] a, int[] b, int left, int right){
		int mid;

		if(left < right){
			//trovo la meta'
			mid = (left + right) / 2;
			//applico la ricorsione e spezzo in 2 l'array
			merge_sort(a, b, left, mid);
			merge_sort(a, b, mid+1, right);
			//rimetto assieme gli array
			merge(a, b, left, mid+1, right);
		}
	}

	public static void merge_sort(int[] a){
		int[] b = new int[a.length];
		merge_sort(a, b, 0, a.length -1);

	}


	public static void merge(int a[], int b[], int left, int center, int right){
		int end1 = center -1; //indice di dove finisce il primo array
		int j = left; //da dove parto con b
		int n = right - left + 1; //numero di elementi

		//scansione array
		while(left <= end1 && center <= right){
			//copio il minore nella prima posizione libera di b
			if(a[left] <= a[center]){
				b[j++] = a[left++];
			} else {
				b[j++] = a[center++];
			}
		}

		//fondo la prima parte
		while(left <= end1 ){
			b[j++] = a[left++];
		}
		while(center <= right){
			b[j++] = a[center++];
		}

		//copio l'array
		for (int i= 0; i < n; i++, right--){
			a[right] = b[right];
		}
	}

}