Java Utililty Methods Collection Concatenate

if (collections == null || collections.length == 0) {
    return Collections.emptyList();
if (collections.length == 1) {
    return collections[0];
return concat(Arrays.asList(collections));

final List<T> concatenation = new ArrayList<T>();
for (final Collection<T> collection : collections) {
    if (collection != null) {
        concatenation.addAll(collection);
return concatenation;

final List<T> concatenation = new ArrayList<T>();
for (final Collection<T> collection : collections) {
    if (collection != null) {
        concatenation.addAll(collection);
return concatenation;

StringBuilder sb = new StringBuilder();
for (Object arg : args) {
    sb.append(separator).append(arg);
if (sb.length() > 0) {
    sb.delete(0, separator.length());
return sb.toString();
...

String[] array = Arrays.copyOf(first, first.length + second.size());
Iterator<String> it = second.iterator();
for (int i = first.length; i < array.length; i++)
    array[i] = it.next();
return array;

StringBuilder sb = new StringBuilder(collection.size());
for (String s : collection) {
    sb.append(String.valueOf(s));
return sb.toString();

final StringBuilder builder = new StringBuilder();
if (c.isEmpty()) {
    return builder;
final Iterator<?> oIterator = c.iterator();
builder.append(oIterator.next());
while (oIterator.hasNext()) {
    builder.append(separator).append(oIterator.next());
...

ArrayList concatenation = new ArrayList();
for (Iterator i = collections.iterator(); i.hasNext();) {
    Collection collection = (Collection) i.next();
    concatenation.addAll(collection);
return concatenation;

StringBuilder sb = new StringBuilder();
Iterator<?> it = coll.iterator();
while (it.hasNext()) {
    sb.append(it.next());
    if (it.hasNext()) {
        sb.append(' ');
return sb.toString();

return concatenate(list, DEFAULT_DELIMITER);