Capital letters are between a and z, lowercase letters are between a and z, and character shaping is between 0 and 9. Just make a judgment. The string knowledge points used, the traversal string, the length method and the toCharArray method for converting char data types. According to normal writing habits, the first letter of an English sentence needs to be capitalized. Capitalization of the first letter in a string can be achieved by the method of strtitle.