indexOf(String str, int fromIndex)
Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.50是查找的起始位置
Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.50是查找的起始位置
s.indexof('a',10),not s.lastindexof('a',10)
but last occurrent of 'a'if
s.lastindexof('a')