import java.util.*;

public class foo {

    public static void main(String[] a) {
        Collection<Double> c = new HashSet<Double>();

        for(int i = 1; i <= 5; i++)
            c.add( (double)i );  // add element to collection

        if ( ! c.isEmpty() ) 
            System.out.println("c has " + c.size() + " elements");

        
        for(Double d : c )     // iterate through a collection!
            System.out.println("c has " + d );
    }

}