Why StringJoiner when we already have StringBuilder?

Question

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

Answer 1

It may simplify your code in some use cases:

List list = // ...;

// with StringBuilder
StringBuilder builder = new StringBuilder();
builder.append("[");
if (!list.isEmpty()) {
    builder.append(list.get(0));
    for (int i = 1, n = list.size(); i < n; i++) {
        builder.append(",").append(list.get(i));
    }
}
builder.append("]");

// with StringJoiner
StringJoiner joiner = new StringJoiner(",", "[", "]");
for (String element : list) {
    joiner.add(element);
}