Why does the Collections class contain standalone (static) methods, instead of them being added to the List interface?

Question

For all the methods in Collections that take a List as their first argument, why aren\'t those methods simply part of the List interface?

My intuition is: given a List

Answer 1

There are two explanations here:

1. Historical: Collections class was created after List interface. Designers chose to preserve backward compatibility of already existing interface. Otherwise a lot of developers would have to change their code.

2. Logical: The methods you are talking about do not require internal knowledge on List implementation and can be implemented over ANY collection implementing it.