Make use of Collections.isEmpty(Iterable) where applicable

[danieldietrich]

I think there are several methods than can be optimized.

For example CharSeq containts the following method:

@Override
public CharSeq prependAll(Iterable<? extends Character> elements) {
    Objects.requireNonNull(elements, "elements is null");
    final StringBuilder sb = new StringBuilder();
    for (char element : elements) {
        sb.append(element);
    }
    sb.append(back);
    return sb.length() == 0 ? EMPTY : of(sb);
}

It can be optimized like this:

@Override
public CharSeq prependAll(Iterable<? extends Character> elements) {
    Objects.requireNonNull(elements, "elements is null");
    if (Collections.isEmpty(elements)) {
        return this; // 1
    } else if (isEmpty()) {
        return CharSeq.ofAll(elements); // 2
    } else {
        final StringBuilder sb = new StringBuilder();
        for (char element : elements) {
            sb.append(element);
        }
        sb.append(back);
        return CharSeq.of(sb);
    }
}

Notes:

• 1: We save a StringBuilder instance, and some (empty) operations and checks
• 2: Same benefits as in 1. Also CharSeq.ofAll does contain additional optimizations, like instanceof CharSeq-shortcut etc.