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.
Throws:
NullPointerException - if str is null.