about String indexOf() method.

[Guoqiao Sun]

Dear all, plz consider the following code:

public class Test095
{    
    public static void main(String args[])
    {
        System.out.println("Java".indexOf(""));
        System.out.println("Java".indexOf("J"));
    }
}

The o/p is

0
0

Why? please give some explanation.
Guoqiao

[Jane Griscti]

Hi Guoqiao,
The API for <code>String.indexOf()</code> states that:

Returns the index within this string of the first occurrence of
the specified substring. The integer returned is the smallest    value k such that: 
                this.startsWith(str, k)
                
is true.

And the API for <code>String.startsWith()</code> states:

Note also that true will be returned if the argument is an empty
string

The net effect is that if an empty string is passed to <code>indexOf</code> the smallest value of <code>k</code> is <code>0</code> and that is returned as the result.
This isn't very clear just from the API but it is confirmed in the Java Class Libraries:Second Edition, Volume 1</code>
Hope that helps.
------------------
Jane Griscti
Sun Certified Programmer for the Java� 2 Platform

[Guoqiao Sun]

Jane, thank you very much for your detailed and swift reply.
I got it now.
Guoqiao

Originally posted by Jane Griscti: