Making a generic comparator class

Question

I'm trying to make a comparator that can take any type of an element to compare. I'm unsure about how to create the class. I just want it to compare two elements of the same type (But whatever type the client gives it, ex: Integer, String, Double, etc...) to see which one is greater then the other.

public class InsertionComparator implements Comparator<T>
{
/**
 * Compares two elements.
 * 
 * @param  f1  The first element you want to compare.
 * @param  f2  The second element you want to compare.
 * @return  -1,0,1  Whether or not one is greater than, less than,
 * or equal to one another.
 */
public int compare(<T> element1,<T> element2)
{
    if(element1 < element2)
    {
        return -1;
    }
    else
    {
        if(element1 > element2)
        {
            return 1;
        }
        else
        {
            return 0;
        }
    } 
}
}

Please help, thank you!

Answer 1

The closest thing you can do to this is a Comparator that can compare any objects that implement the Comparable interface:

class NaturalComparator<T extends Comparable<T>> implements Comparator<T> {
  public int compare(T a, T b) {
    return a.compareTo(b);
  }
}

That's really the closest you can do: only Comparable objects have the "natural ordering" you're trying to model here. But generally, once you have Comparable objects, you don't necessarily need a Comparator: for example, Collections.sort can take either a List with a Comparator, or a List with Comparable elements.