Java Utililty Methods Array Join

if (strings == null) {
    return null;
final int length = strings.length;
if (length == 0) {
    return STR_EMP;
final int sepLen;
...

return join(sep, Arrays.asList(os));

if (a.length == 0)
    return "";
if (a.length == 1)
    return a[0];
StringBuffer sbuff = new StringBuffer();
sbuff.append(a[0]);
for (int i = 1; i < a.length; i++) {
    if (sep != null)
...

if (arr == null)
    return null;
StringBuilder str = new StringBuilder();
for (int i = 0; i < arr.length; i++)
    str.append(i == 0 ? arr[i] : sep + arr[i]);
return str.toString();

return join(separator, Arrays.asList(array));

return join(separator, strings, 0, strings.length);

return join(separator, strings, 0, strings.length);

try {
    Collection<String> s = Arrays.asList(a);
    StringBuffer buffer = new StringBuffer();
    Iterator<String> iter = s.iterator();
    while (iter.hasNext()) {
        if (startIndex == 0) {
            buffer.append(iter.next());
            if (iter.hasNext()) {
...

String[] temp = new String[a.length + b.length];
System.arraycopy(a, 0, temp, 0, a.length);
System.arraycopy(b, 0, temp, a.length, b.length);
Arrays.sort(temp); 
return temp;

List<String> result = new ArrayList<>();
result.addAll(Arrays.asList(a1));
result.addAll(Arrays.asList(a2));
return result.toArray(new String[0]);