I need make a merge sort using an additional array. Here is my code:

public class extra_storage{  
    public static void main(String[]args) { 

        int x[]=new int[]{12,9,4,99,120,1,3,10};
        int a[]=new int[x.length];

        mergesort(x,0,x.length-1,a);
        for (int i=0;i<x.length;i++){
            System.out.println(x[i]);
        }       
    }

    public static void mergesort(int x[],int low,int high, int a[]){      
        if (low>=high) {
            return;
        }
        int middle=(low+high)/2;
        mergesort(x,low,middle,a);
        mergesort(x,middle+1,high,a);
        int k;
        int lo=low;
        int h=high;
        for (k=low;k<high;k++)
            if ((lo<=middle ) && ((h>high)||(x[lo]<x[h]))){
                a[k]=x[lo++];
            }
            else {
                a[k]=x[h++];
            }
        for (k=low;k<=high;k++){
            x[k]=a[k];
        }     
    }
}

But something is wrong. When I run it the output is this:

1
0
3
0
4
0
9
0

What is the problem?