Java Interface Comparator static compare

Question

int compare(Object o1, Object o2) Compares its two arguments for order.

For compare 2 objects o1 and o2 need do something like:

MyClass o1=new MyClass();
MyClass o2=new MyClass();

 if (o1.compare(o1,o2)>0) ......

Why this methtod not static? If method was static possible like:

 if (MyClass.compare(o1,o2)>0) ....

Answer 1

If it were static, how could it be called polymorphically? The point of Comparator is that you can pass an instance into something like sort... which has to then call the compare method on the comparator instance.

If a class is capable of comparing one instance of itself to another, it should implement Comparable instead, so you'd write:

if (o1.compareTo(o2))

Answer 2

Your question shows a lack of understanding of Comparable and Comparator.

A Comparator is capable of comparing two other objects;

MyClass o1 = new MyClass();
MyClass o2 = new MyClass();
MyComparator c1 = new MyComparator();

if (c1.compare(o1, o2) > 0) {
  ...
}

Something which is Comparable is able to be compared to other objects;

MyClass o1 = new MyClass();
MyClass o2 = new MyClass();

if (o1.compareTo(o2)) > 0) {
  ...
}

It is very rare to compare a Comparator, so your example;

if (o1.compare(o1, o2) > 0) {
  ...
}

doesn't really make sense. Anyway, onto the answer, why isn't compareTo() static? Basically, Comparator is an interface, and interfaces can't have static methods. Why? Well, it doesn't make sense for them. An interface is about defining a contract, but providing no implementation.