import java.util.*;
public class PolymorphicCollectionExample{
	//Here we choose what collection to make
	public static Collection makeCollection(boolean sorted){
		if(sorted) return new TreeSet();
		else return new HashSet();
	}
	//Here we can use the Collection without knowing its //concrete type
	public static void main(String[] args){
	  Collection col = makeCollection(true);
	  col.add(new Integer(1));
	  col.add(new Integer(2));
	  col.add(new Integer(3));
	  col.add(new Integer(4));
	  System.out.println(col);
	}
}