Returns the index within this string of the first occurrence of the specified character. If a character with value
ch occurs in the character sequence represented by this
String object, then the index of the first such occurrence is returned -- that is, the smallest value
k such that:
this.charAt(k) == ch
is
true. If no such character occurs in this string, then
-1 is returned.
@param ch a character.
@return the index of the first occurrence of the character in thecharacter sequence represented by this object, or
-1 if the character does not occur.