Why StringJoiner when we already have StringBuilder?

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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.

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