Here are the use of some methods in String type, including:

1. Extraction of elements in string;
2. Appending of elements in string;
3. String ignore case for comparison;
4. Conversion of Chinese and English letters in string;
5. Get string length;
6. Replace the element or substring in the string;
7. String truncation;
8. Eliminate the first and last space characters in the string;
9. Insert a new character or string into the string;
10. Reverse the order of characters in the string;

The following ten methods are demonstrated in the same procedure:

/**
 * Learning supplement · String
 * @author Turn off the lock
 */
public class Yushu {
    public static void main(String[] args) {
        /*
         * charAt Method can extract the elements in the string concat method can append the string
         */
        String str = "This is the first";
        System.out.println(str.charAt(3));
        String ing = "A complete sentence.";
        String string = str.concat(ing + "(It's used here concat Method)");
        System.out.println(string);
        String str1 = " The moon shines among the pines, and the clear spring stone flows upward.(call trim()Method to remove spaces at the beginning and end of a string) ";
        StringBuffer part1 = new StringBuffer("Houyuxinshankong");
        part1.reverse();// The reverse() method reverses the order of all characters in a string without defining a new variable to receive them
        System.out.println(part1);
        part1.append("Come autumn.");// The StringBuffer append() method can be used to connect strings
        part1.insert(5, ",It's late");// StringBuffer insert() method can be used to insert elements
        /*
         * insert Method must have two parameters: 1. Insert location; 2. Insert element
         * When the element "boolean" needs to be inserted, the insertion part must write "boolean.class" to be valid
         * If you are inserting other data types, you need to insert them according to the writing format of their data types 
         * For example: char type must use single quotation marks, and can also insert variables, arrays, etc
         * Note, however, that there is an order of insertion
         */
        int array[] = new int[] { 8, 37 };
        part1.insert(4, 64);
        part1.insert(3, boolean.class);
        part1.insert(7, array);
        System.out.println(part1);
        String y = str1.trim();// The trim() method is used to delete spaces at the beginning and end of a string
        System.out.println(y);
        /*
         * substring()Method to intercept a string from beginIndex to endIndex in a string
         * Where, endIndex can be left blank, which means to intercept the string after beginIndex
         * In addition, select the part that needs multiline annotation, and use control+shift + / to make quick multiline annotation
         */
        String z = y.substring(6, 10);
        System.out.println(z);
        String s00 = "wElcOme To";
        String s01 = "WeLCoMe tO";
        // Use the length() method to get the length of the string
        System.out.println(s00.length());
        /*
         * toLowerCase()And str02=s02.toUpperCase() method can perform case conversion
         * But it should be noted that the case conversion here converts the case of Chinese and English letters in the whole string
         */
        String str01 = s01.toLowerCase();
        // Using the equalsIgnoreCase() method, you can compare strings regardless of the case of English letters. The result is a boolean type
        System.out.println(s00.equalsIgnoreCase(s01));
        String s02 = " heut!";
        /*
         * Use the replace() method to replace the elements in a string (including a single character of char type and a string of multiple characters connected)
         * Note: when replacing consecutive substrings in a string, the substring to be replaced must be the connected part of the original string.
         * But when replacing a substring, you can replace it with a different length
         */
        String s03 = s02.replace('e', 'a');
        String s04 = s02.replace("heut", "Turn off the lock");
        System.out.println(s04);
        String str02 = s03.toUpperCase();
        System.out.println(str01 + str02);
    }
}

Attached with output rendering: