Why are the 'Arrays' class' methods all static in Java?

Question

I was going through Java documentation, and I learned that methods in the Arrays class in Java are all static. I don't really understand the reason behind why they made it static.

For example, the following code violates the OO approach, because if I have a type, 'X', then all the methods which acts on it should be inside it:

int[] a = {34, 23, 12}; Arrays.sort(a); 

It would be better if they have implemented the following way:

int[] a = {34, 23, 12}; a.sort(); 

Can anyone explain me a bit on this?

Answer 1

In Java there is no way to extend the functionally of an array. Arrays all inherit from Object but this gives very little. IMHO This is a deficiency of Java.

Instead, to add functionality for arrays, static utility methods are added to classes like Array and Arrays. These methods are static as they are not instance methods.

Answer 2

Good observation. Observe also that not every array can be sorted. Only arrays of primitives and Objects which implement the Comparable interface can be sorted. So a general sort() method that applies to all arrays is not possible. And so we have several overloaded static methods for each of the supported types that are actually sortable.

Update:

@Holger correctly points out in the comments below that one of the overloaded static methods is indeed Arrays.sort(Object[]) but the docs explicitly state:

All elements in the array must implement the Comparable interface.

So it doesn't work for Objects that don't implement Comparable or one of its subinterfaces.