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When to use StringJoiner over StringBuilder?

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Prerequisite: StringJoiner
StringJoiner is very useful, when you need to join Strings in a Stream. 
Task : Suppose we want the string “[George:Sally:Fred]”, where we have given a string array that contains “George”, “Sally” and “Fred”.
StringJoiner provide add(String str) method to concatenate the strings based on supplied delimiter,prefix and suffix in the constructor, but if we use StringBuilder to perform our task then first we have to append prefix and then iterate through string array and append the required delimiter after each element and finally append the prefix. Below is the java program to demonstrate both ways.


// 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
        // converting StringJoiner to String
        String desiredString = sj.toString();
        // By using StringBuilder class
        // declaring empty stringbuilder
        StringBuilder sb = new StringBuilder();
        // appending prefix
        // checking for empty string array
            // appending first element
            // iterating through string array
            // and appending required delimiter
            for (int i = 1; i < str.length; i++)
        // finally appending suffix
        // converting StringBuilder to String
        String desiredString1 = sb.toString();



This article is contributed by Gaurav Miglani. If you like GeeksforGeeks and would like to contribute, you can also write an article using or mail your article to See your article appearing on the GeeksforGeeks main page and help other Geeks.
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Last Updated : 11 Aug, 2021
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