Joins an array or Iterable into an existing Appendable like a StringBuilder; with the goal for call sites to avoid creating intermediary Strings. This is like String#join(CharSequence, CharSequence...), String#join(CharSequence, Iterable), and StringJoiner.

Keep an instance in a (static) variable for efficient joining into an Appendable or StringBuilder without creating temporary Strings.

Use the builder and instance methods to reuse the same kind of joining prefix, suffix, delimiter, and string conversion.

For example:

// A reuseable instance
private static final AppendableJoiner<Object> JOINER = AppendableJoiner.builder()
    .setPrefix("[")
    .setSuffix("]")
    .setDelimiter(", ")
    .get();

...
// Builds straight into a StringBuilder:
StringBuilder sbuilder = new StringBuilder("1");
JOINER.join(sbuilder, "A", "B");
sbuilder.append("2");
JOINER.join(sbuilder, "C", "D");
sbuilder.append("3");
// Returns "1[A, B]2[C, D]3"
return sbuilder.toString();
}

To provide a custom Object element to CharSequence converter, call Builder#setElementAppender(FailableBiConsumer), for example:

private static final AppendableJoiner<Item> JOINER = AppendableJoiner.builder()
    .setElementAppender(e -> (a, e) -> a.append(e.getFoo())
                                       a.append(e.getBar())
                                       a.append('!'))
    ...
    .get();

}

This class is immutable and thread-safe.