Summary of common methods of string:

1. Use charAt() Method can get the character of the position of the index value corresponding to the string , Parameter is int String subscript of type , The return value type is char type .

2. Use compareTo() Method can compare the size of the current string with another string , Parameter is String String of type , The return value type is int type .

3. Use contains() Method can determine whether the current string contains a parameter string , The parameter is an interface type CharSequence, The return value type is boolean type . Return if present true, Returns if it does not exist false.

4. Use equals() Method to compare whether the contents of two strings are the same , Parameter is Object class , That is, you can pass any type of parameter , The return value type is boolean type , If the contents are equal, return true, Unequal return false. 

5. Use equalsIgnoreCase() The method is to ignore case （ English letter ） Comparison , Parameter is String type , The return value is boolean type . After ignoring case , If the contents are equal, return true, Unequal return false.

6. Use startsWith() and endsWith() Method can determine whether the atomic character string starts or ends with the parameter string , Parameter is String type , The return value is boolean type , If it starts with a parameter string, it returns true, Otherwise return to false.

7. Use indexOf() Method can find the position where the parameter string first appears , The return value is int type , If it exists, the subscript position of the first occurrence of the string is returned , Otherwise return to -1.

8. Use lastIndexOf() Method can find the position of the last occurrence of the parameter string , The return value is int type , If it exists, it returns the subscript of the last occurrence of the string , Otherwise return to -1.

9. Use length() Method can get the length of the current string , The return value is int type .

10. Use replace() Method can replace string , The return value is String type . 

11. Use split() Method to split a string , Parameter is String type , The return value is String[] Array

12. Use substring() Method intercepts the string , Parameter is int type , The return value is String type

13. Use toCharArray() Method converts the current string into an array of character types , The return value is char[] Type array

14. Use toLowerCase() or toUpperCase() Convert all letters to lowercase or uppercase , The return value is String type

15. Use trim() You can remove the first and last white space characters of the string , Include \t,\r,\n, The return value is String type

16. Use format() Format array output , Pass in the parameter , Replace placeholders , Generate a new string , The return value is String type

17. Use join() Method is used to splice strings , The return value is String type

18. Use valueOf() Method can convert any reference type or basic type to string type , The return value is String type