1.charAt() returns the character at the specified index.
String s="1234567890";
char t=s.charAt(9);
System.out.println(t);
//输出t=0
2.equals compares whether two strings are exactly the same (content + address)
3.equalsIgnoreCase does not consider case comparison
4.getBytes() method has two forms
getBytes(String charsetName): Use the specified character set to encode the string into a byte sequence, and store the result in a new byte array.
getBytes(): Use the platform's default character set to encode the string into a byte sequence, and store the result in a new byte array.
5.length() string length
6. getchars() intercepts multiple characters and receives them by other strings
7. toCharArray() turns a string into a character array
8. startsWith() and endsWith() determine whether the string starts or ends with a specific character
9. toUpperCase() and toLowerCase() convert the string to uppercase or lowercase
10. concat() connect two strings
11. trim() to remove the starting and ending spaces
12. substring() intercepts the string
13. IndexOf() and lastIndexOf() The former is to find the first occurrence of a character or string, and the latter is to find the last occurrence of a character or string
14. replace() Replace
15. compareTo() and compareToIgnoreCase() compare the size of two strings in lexicographical order, the former is case sensitive, the latter is not