Java inserts new characters or strings into original characters

Insert character code:

public class Test {
      
	  /**Insert new characters in the original characters**/
      public static void main(String[] args){
    	 
    	  StringBuffer sb = new StringBuffer("Tiantian is a girl!");//Create a character cache area, and the content in the cache area is "Tiantian is a girl!"
    	  ("The content in the original character cache is: "+sb);//Output the content in the original character cache
    	  ("The length in the original character buffer is: "+() );//Length
    	  ("The capacity in the original character cache is: "+() );//Capacity
    	 
    	  (5, 'small');// Assign a new value to the value before the specified subscript position
    	 
    	  ("The content in the new character cache is: "+sb);//Output the content in the new character cache
    	  ("The length in the new character cache is: "+() );//Length
    	  ("The capacity in the new character cache is: "+() );//Capacity
    	 
    
      }
       
 }

explain: (5, ‘small’);// Assign a new value to the value before the specified subscript position, which means inserting the word ‘small’ before the 6th character of sb. 5 is the position of the subscript in the character buffer area, and the same as the array starts from 0.

Running results:

The content in the original character cache area is: Tian Tian is a girl!
 The length in the original character cache is: 8
 The capacity in the original character cache is: 24
 The content in the new character cache is: Tiantian is a little girl!
 The length in the new character cache is: 9
 The capacity in the new character cache is: 24

/*********************************************************************************************/
/*********************************************************************************************/

Insert string code:

public class Test {
     
	  /**Insert new characters in the original characters**/
      public static void main(String[] args){
    	 
    	  StringBuffer sb = new StringBuffer("Tiantian is a girl!");//Create a character cache area, and the content in the cache area is "Tiantian is a girl!"
    	  ("The content in the original character cache is: "+sb);//Output the content in the original character cache
    	  ("The length in the original character buffer is: "+() );//Length
    	  ("The capacity in the original character cache is: "+() );//Capacity
    	 
    	  (5, "Just 18 years old");// Assign a string to the value before the specified subscript position
    	 
    	  ("The content in the new character cache is: "+sb);//Output the content in the new character cache
    	  ("The length in the new character cache is: "+() );//Length
    	  ("The capacity in the new character cache is: "+() );//Capacity
    	 
    
      }
       
 }

Running results:

The content in the original character cache area is: Tian Tian is a girl!
 The length in the original character cache is: 8
 The capacity in the original character cache is: 24
 The content in the new character cache is: Tiantian is a girl who just turned 18!
 The length in the new character cache is: 14
 The capacity in the new character cache is: 24

Summarize:

(5, 'small') is to insert the word 'small' before the 6th character of the string sb;
  (5, "Just 18 years old"); is to insert the string "Just 18 years old" before the 6th character of the string sb;
  Note: Use ‘’, and use ‘’ in strings.