Java String.indexOf and empty Strings

Question

I\'m curious why the String.indexOf is returning a 0 (instead of -1) when asking for the index of an empty string within a string.

The Javadocs only say this method

Answer 1

By using the expression "", you are actually referring to a null string. A null string is an ethereal tag placed on something that exists only to show that there is a lack of anything at this location.

So, by saying "".indexOf( "" ), you are really asking the interpreter:

Where does a string value of null exist in my null string?

It returns a zero, since the null is at the beginning of the non-existent null string.

To add anything to the string would now make it a non-null string... null can be thought of as the absence of everything, even nothing.