sorting via Merge Sort algorithm - sorting

Question

This is the merge sort program. I traced this program and found that after sorting the first four elements of array, the recursive call to sort function with left array with elements 4,6 again gets executed which increments 'k' to upper bound and throws ArrayIndexOutofBound index. I am not able to figure out the complete flow. please help.
class MergeSort
{
static int k=0;
static int a[]={2,1,4,6,8,5,3,9};
public static void main(String args[])
{
int i;
System.out.println("Before");
for(i=0;i<a.length;i++)
{
System.out.print(a[i]+" ");
}
System.out.println("\n");
sort(a);
System.out.println("\nAfter");
for(i=0;i<a.length;i++)
{
System.out.print(a[i]+" ");
}
System.out.println("\n");
}
public static void sort(int b[])
{
int n=b.length;
if(n<2)
return;
int mid=n/2;
int left[]=new int[mid];
int right[]=new int[n-mid];
int i;
System.out.print("left ");
for(i=0;i<mid;i++)
{
left[i]=b[i];
System.out.print(left[i]+" ");
}
System.out.println();
System.out.print("right ");
for(i=mid;i<n;i++)
{
right[i-mid]=b[i];
System.out.print(right[i-mid]+" ");
}
System.out.println("\n");
sort(left);
sort(right);
merge(left,right);
}
public static void merge(int l[], int r[])
{
int i=0;
int j=0;
while(i<l.length && j<r.length)
{
if(l[i] < r[j]){
a[k]=l[i];
System.out.println("a["+k+"]="+a[k]);
i++;
}
else
{
a[k]=r[j];
System.out.println("a["+k+"]="+a[k]);
j++;
}
k++;
}
while(i<l.length)
{
a[k]=l[i];
System.out.println("a["+k+"]="+a[k]);
i++;
k++;
}
while(j<r.length)
{
a[k]=r[j];
System.out.println("a["+k+"]="+a[k]);
j++;
k++;
}
}
}