Question: I need a comparator as part of a strategy pattern that can either use the natural ordering of the objects or some custom ordering. For the natural ordering case, I wrote a simple comparator:

```
private static class NaturalComparator<T extends Comparable<? super T>> implements Comparator<T> {
    @Override
    public int compare(T o1, T o2) {
        return o1.compareTo(o2);
    }
}

```

Seems simple enough, but I was wondering if anyone knew of one in the standard API. I looked at TreeMap, and it does it without such a class, so when that code was written, the apparent answer would be no, but perhaps it was added later.

Answer: 
Added to [Comparator in Java 8](https://docs.oracle.com/javase/8/docs/api/java/util/Comparator.html#naturalOrder--):

```
static <T extends Comparable<? super T>> Comparator<T> naturalOrder()

```

Use it like this, for example:

```
Comparator<Double> natural = Comparator.<Double>naturalOrder();
return natural.compare(1.0, 1.1));

```
I think if a class has a natural ordering, it is more usual in Java for it to implement `Comparable` rather than have a `Comparator` implementation for each class.

Thus, if the objects in question have a natural ordering defined, they must implement `Comparable` and have the `compareTo` method defined. No need to go looking for a `Comparator`. Most classes in java.util take either an optional `Comparator` if there is any specific ordering to be imposed, or simply try to call `compareTo` on the objects if there is no other ordering specified.

So, long story short: Implement `Comparable` whenever you want to impose a natural ordering on a class, only use a `Comparator` when you want something other than the natural ordering.