how to generate a MST random graph so same edge will not come again

i want to create a graph using random number. Edges will be taken from random number. But when i created this, duplicate edges like 4-1 and 1-4 comes. As it's undirected graph it'll create problem for giving weights.

my code:

 public class Edge
 {
public static void main(String[] args)
{ 
   Random random = new Random();

    int v,e;

    Scanner sc=new Scanner(System.in);

  System.out.println("input vertex");

  v=sc.nextInt();

 System.out.println("input edge");

 e=sc.nextInt();

for(int i = 1; i <= e; i++) {

  String y= Integer.toString(random.nextInt(v));

  int y1 = Integer.parseInt(y)+1;


String x=  Integer.toString(random.nextInt(v));

 int x1 = Integer.parseInt(x)+1;

 if(x1==y1){

     i--;
    }

else
   System.out.println("  "+y1+"  "+x1);    }     }}

 output:

 node 4 edge 6

   2  4
   2  3
   4  1
   4  3
   1  2
   3  2

as 2-3 and 3-2 came twice how to give condition here