jodd-core/src/main/java/jodd/util/StringUtil.java
public static String join(final Collection collection, final char separator) {
		if (collection == null) {
			return null;
		}

		if (collection.size() == 0) {
			return StringPool.EMPTY;
		}

		final StringBuilder sb = new StringBuilder(collection.size() * 16);
		final Iterator it = collection.iterator();

		for (int i = 0; i < collection.size(); i++) {

			if (i > 0) {
				sb.append(separator);
			}

			sb.append(it.next());
		}

		return sb.toString();
	}
public static String join(final Collection collection, final char separator) {
		if (collection == null) {
			return null;
		}

		if (collection.size() == 0) {
			return StringPool.EMPTY;
		}

		final StringBuilder sb = new StringBuilder(collection.size() * 16);
		final Iterator it = collection.iterator();

		for (int i = 0; i < collection.size(); i++) {

			if (i > 0) {
				sb.append(separator);
			}

			sb.append(it.next());
		}

		return sb.toString();
	}
Joins an collection of objects into one string with separator.