When to use StringJoiner over StringBuilder?

// Java program to demonstrate use of 
// StringJoiner class over StringBuilder class

import java.util.StringJoiner;

public class Test 
{
    public static void main(String[] args)
    {
        // given string array
        String str[] = {"George","Sally","Fred"};
            
        // By using StringJoiner class
            
        // initializing StringJoiner instance with
        // required delimiter, prefix and suffix
        StringJoiner sj = new StringJoiner(":", "[", "]");
            
        // concatenating strings
        sj.add("George").add("Sally").add("Fred");
            
        // converting StringJoiner to String
        String desiredString = sj.toString();
            
        System.out.println(desiredString);
            
        // By using StringBuilder class
            
        // declaring empty stringbuilder
        StringBuilder sb = new StringBuilder();
            
        // appending prefix
        sb.append("[");
            
        // checking for empty string array
        if(str.length>0)
        {
            // appending first element
            sb.append(str[0]);
                
            // iterating through string array 
            // and appending required delimiter
            for (int i = 1; i < str.length; i++) 
            {
                sb.append(":").append(str[i]);
            }
        }
            
        // finally appending suffix
        sb.append("]");
            
        // converting StringBuilder to String
        String desiredString1 = sb.toString();
            
        System.out.println(desiredString1);
    }
}