Why StringJoiner when we already have StringBuilder?

java string java-8 stringbuilder
Hitesh Garg picture Hitesh Garg · Dec 17, 2014 · Viewed 41.6k times · Source

I recently encountered with a Java 8 class StringJoiner which adds the String using the delimiters and adds prefix and suffix to it, but I can't understand the need of this class as it also uses StringBuilder at the backend and also performs very simple operation of appending the Strings.

Am I missing something by not actually understanding the real purpose of this class?

Answer

Martin Seeler picture Martin Seeler · Dec 17, 2014

StringJoiner is very useful, when you need to join Strings in a Stream.

As an example, if you have to following List of Strings:

final List<String> strings = Arrays.asList("Foo", "Bar", "Baz");

It is much more simpler to use

final String collectJoin = strings.stream().collect(Collectors.joining(", "));

as it would be with a StringBuilder:

final String collectBuilder =
    strings.stream().collect(Collector.of(StringBuilder::new,
        (stringBuilder, str) -> stringBuilder.append(str).append(", "),
        StringBuilder::append,
        StringBuilder::toString));

EDIT 6 years later As noted in the comments, there are now much simpler solutions like String.join(", ", strings), which were not available back then. But the use case is still the same.

Related questions

Why is String.chars() a stream of ints in Java 8?

In Java 8, there is a new method String.chars() which returns a stream of ints (IntStream) that represent the character codes. I guess many people would expect a stream of chars here instead. What was the motivation to design the …

Read More
Java 8 Comparator nullsFirst naturalOrder confused

this may be a simple question but I would like to understand it clearly... I have a code like this: public final class Persona { private final int id; private final String name public Persona(final int id,final String name) { …

Read More
How do I convert a String to an int in Java?

How can I convert a String to an int in Java? My String contains only numbers, and I want to return the number it represents. For example, given the string "1234" the result should be the number 1234.

Read More