indexOf() in java

Question

Why in the syntax "int indexOf(int ch)" the type of ch is "int".
It should be rather "char" because here we are searching for character and not an integer.

Answer 1

I think for handling Unicode chars

Answer 2

then why in the syntax "int indexOf(String str)" type of str is String and not integer

Answer 3

Becauae you want get index of a substring 😉