Confusion about indexOf method

[Rd Dari]

Hi,
There is a snippet of code:

String s;
int a;
s = "Foolish boy.";
a = s.indexOf("fool");

Options of the output are:-

a) -1
b) 0
c) 4
d) random value

and the output of the code is : -1

How it is working please explain it.

Thank you

[marc weber]

String's indexOf method returns -1 if the substring is not found. I don't see a (lowercase) 'f' in "Foolish".

[Rd Dari]

ok but if there is

a = s.indexOf("Fool");

then what output should be:

[Wouter Oet]

Try it and find out.

[Sergey Baranov]

indexOf

public int indexOf(String str)
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.

Parameters:
str - any string.

Returns:
if the string argument occurs as a substring within this object, then the index of the first character of the first such substring is returned; if it does not occur as a substring, -1 is returned.

[Rd Dari]

Hi Wouter Oet ,


I run this program and output is 0.

But actually I am not understanding that how it works so please give me some explanation which will helpful for me to understand it easily.

Thanks in advance....

[fred rosenberger]

the positions of "Foolish" are counted like this:

F -> 0
o -> 1
o -> 2
l -> 3
i -> 4
s -> 5
h -> 6

So, "Fool" matches starting at the 0th position.

[Jesper de Jong]

The indexOf() method searches in the string that you call it on, where the string that you pass as an argument appears - exactly what the API documentation that Sergey quoted says.

The word "Fool" appears in the string "Foolish boy." at the beginning - index 0.

Can you explain in more detail what exactly you don't understand about that?

[Rd Dari]

Yes Jasper,

In actual I was confused that how it matches to subString but Thank you of all you for giving me a good explanation I understand now this so thank you once again...............