Java Utililty Methods Array Concatenate

if (first == null && second == null) {
    return new int[0];
if (first == null) {
    return Arrays.copyOf(second, second.length);
if (second == null) {
    return Arrays.copyOf(first, first.length);
...

assert arrays != null;
assert arrays.length > 1;
int len = 0;
for (int[] a : arrays)
    len += a.length;
int[] r = Arrays.copyOf(arrays[0], len);
for (int i = 1, shift = 0; i < arrays.length; i++) {
    shift += arrays[i - 1].length;
...

return concat(array, SPACE);

Object[] result = Arrays.copyOf(first, first.length + 1);
System.arraycopy(new Object[] { second }, 0, result, first.length, 1);
return result;

StringBuilder sb = new StringBuilder();
String sep = "";
for (String s : array) {
    sb.append(sep).append(s);
    sep = separator;
return sb.toString();

return Arrays.stream(parts).reduce((a, b) -> a.concat(" ").concat(b)).orElse("");

StringBuilder builder = new StringBuilder();
for (String str : strs) {
    builder.append(str);
return builder.toString();

List<String> result = new ArrayList<String>();
for (String[] p : arrays) {
    for (String x : p) {
        result.add(x);
return result;

List<T> v = new ArrayList<T>(vals.length + 1);
v.add(val);
v.addAll(Arrays.asList(vals));
return v.toArray(vals);

int al = a.length;
int bl = b.length;
T[] c = Arrays.copyOf(a, al + bl);
for (int i = 0; i < bl; i++) {
    c[al + i] = b[i];
return c;