indexOf second argument in Scala-CodePudding

I want to understand what does second argument in indexOf in Scala mean for Strings?

object Playground extends App {
    val g: String = "Check out the big brains on Brad!"
    println(g.indexOf("o",7));
}

The above program returns: 25 which is something I am not able to understand why?

It is actually the index of last o but how is it related to 7? Is it like the second argument n returns the index of the occurence of nth character and if n exceeds with the number of occurences then it returns the index of last present element?

But if that's the case then this doesn't make sense:

object Playground extends App {
    val g: String = "Check out the big brains on Brad!"
    (1 to 7).foreach(i => println(s"$i th Occurence = ${g.indexOf("o",i)} "))
}

which outputs:

1 th Occurence = 6 
2 th Occurence = 6 
3 th Occurence = 6 
4 th Occurence = 6 
5 th Occurence = 6 
6 th Occurence = 6 
7 th Occurence = 25

Source: https://www.scala-exercises.org/std_lib/infix_prefix_and_postfix_operators

CodePudding user response：

According to Scala String documentation, the second parameter is the index to start searching from:

def indexOf(elem: Char, from: Int): Int

Finds index of first occurrence of some value in this string after or at some start index.

elem : the element value to search for.
from : the start index
returns : the index >= from of the first element of this string that is equal (as determined by ==) to elem, or -1, if none exists.

Thus, in your case, when you specify 7, it means that you will look for the index of the first character "o" which is located at index 7 or after . And indeed, in your String you have two "o", one at index 6, one at index 25.

CodePudding user response：

indexOf(int ch, int fromIndex) looks for the character in the string from the specified index (fromIndex). This means it starts looking at 7th position.

CodePudding user response：

Going forward you need to learn to read the official docs: indexOf:

def indexOf(elem: A, from: Int): Int
[use case] Finds index of first occurrence of some value in this general sequence after or at some start index.

Note: may not terminate for infinite-sized collections.

elem
the element value to search for.

from
the start index

returns
the index >= from of the first element of this general sequence that is equal (as determined by ==) to elem, or -1, if none exists.

I personally like to use Intellij to jump into the source code with CMD B.

No matter how you take it: in your development flow you'll frequently access the manual\docs of the lib or lang you're using.