Is there a better way to add int arrays together?

Question

I'm working on a project that will add arrays of integer together...all element are nonnegative integers
For example
A = [0 1 2 3]
I need to find an algorithm to find 2A= A + A, 3A = A+A+A....., hA = A +...A ( h times)
For 2A, the result array will look like this
2A = [ 0 1 2 3 1 2 3 4 2 3 4 5 3 4 5 6]
Then using Array.sort(2A) i will have 2A= [ 0 1 1 2 2 2 3 3 3 3 4 4 4 5 5 6].
Lastly I will write another code to get rid of repetitions to get the desired array 2A = [ 0 1 2 3 4 5 6]
public static int[] hA(int[] a, int h){
   // mon = null;
   //mon = MonitorFactory.start("myFirstMonitor");
       if (h==1) return a;
       if (h==2){          
              int[] b = new int[(a.length)*(a.length)];
           int count = 0;
           int maxa = a.length,maxb=b.length;
           for (int i = 0 ; i < maxa; i++)
           for (int j=0 ; j <maxa; j++)
             b[count]=a[i]+a[j];
                count++;
            return b;
           else
           return hA(a,h-1);     
       }I still don't know how to write recursive code to get it to find 3A, 4A....hA....
is there any better way to do this?

Answer 1

sorry for not defining it better
2A ={ a + a' | a,a' E A}
that means for A = { 0 1 3} , 2A ={ 0 1 2 3 4 6}
but to get to [ 0 1 2 3 4 6], i don't know of any better way to achieve it.
Also to find 3A = { a+a'+a'' |a,a',a'' E A}
that means for A = { 0 1 3} ,3A={ 0 1 2 3 4 5 6 7 9}
the idea is simple but to put into java code is not...at least for me