Missing Number

import java.util.*;;
class rand extends Random
{
 public int generate()
 {
 return nextInt(10);
 }
}
public class Missingnum {
 public static void main(String args[])
 {
 int i;
 int [] a= new int[10];
 rand r1 = new rand();
 HashSet h1= new HashSet ();
 HashSet h2= new HashSet ();

 for (i=0;i<10;i++)
 a[i]=r1.generate();

 for(i=0;i<10;i++)
 h1.add(a[i]);//removes duplicate elements.
 System.out.println("HashSet contains"+ h1);

 for(i=0;i<10;i++)
 if(!h1.contains(i))//add all elements which are not in h1 to h2.
 h2.add(i);

 System.out.println("Numbers not in HashSet"+h2);

 for(i=0;i<10;i++)
 if(!h1.contains(i))//add remaining elements to h1
 h1.add(i);

 System.out.println("Numbers now in HashSet H1"+h1);
}
}