public class Example {

  public Example(int N) // create N-by-N grid, with all sites blocked
  {
    uf = new WeightedQuickUnionUF(N);
  }

  public void foo(int i)
  {
    uf.union(i,i);
  }

  private WeightedQuickUnionUF uf;

  public static void main(String[] args)   // test client (optional)
  {
    Example ex = new Example(5);
    ex.foo(5);
  }
}