利用compareTo实现版本号判断

Compares the specified string to this string using the Unicode values of the characters. Returns 0 if the strings contain the same characters in the same order. Returns a negative integer if the first non-equal character in this string has a Unicode value which is less than the Unicode value of the character at the same position in the specified string, or if this string is a prefix of the specified string. Returns a positive integer if the first non-equal character in this string has a Unicode value which is greater than the Unicode value of the character at the same position in the specified string, or if the specified string is a prefix of this string.Compares the specified string