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 returns the index in this string of the specified string, -1 if the string isn't found.

To me this behavior seems highly unexpected, I would have expected a -1. Any ideas why this unexpected behavior is going on? I would at the least think this is worth a note in the method's Javadocs...

System.out.println("FOO".indexOf("")); // outputs 0 wtf!!!
System.out.println("FOO".indexOf("bar")); // outputs -1 as expected
System.out.println("FOO".indexOf("F")); // outputs 0 as expected
System.out.println("".indexOf("")); // outputs 0 as expected, I think

Answer 1

Well, if it helps, you can think of "FOO" as "" + "FOO".

Answer 2

The empty string is everywhere, and nowhere. It is within all strings at all times, permeating the essence of their being, yet as you seek it you shall never catch a glimpse.

How many empty strings can you fit at the beginning of a string? Mu

The student said to the teacher,

Teacher, I believe that I have found the nature of the empty string. The empty string is like a particle of dust, and it floats freely through a string as dust floats freely through the room, glistening in a beam of sunlight.

The teacher responded to the student,

Hmm. A fine notion. Now tell me, where is the dust, and where is the sunlight?

The teacher struck the student with a strap and instructed him to continue his meditation.

Answer 3

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.