What's the difference between instance method reference types in Java 8?

1. myString::charAt would take an int and return a char, and might be used for any lambda that works that way. It translates, essentially, to index -> myString.charAt(index).

2. String::length would take a String and return an int. It translates, essentially, to string -> string.length().

3. String::charAt would translate to (string, index) -> string.charAt(index).

With this they mean that you have the following:

1) Can be for example this::someFunction;, this will return the someFunction reference of the current object.

2) Can be for example String::toUpperCase, this will return the toUpperCase method of String in general.

I am not sure if there is an actual difference in behaviour, I think it is just like you can also call static methods on instance variables.