code: public static String[] concatenateStringArrays(String[] array1,
                                                     String[] array2) {
          if (isEmpty(array1)) {
              return array2;
          }
          if (isEmpty(array2)) {
              return array1;
          }
          String[] newArr = new String[array1.length + array2.length];
          System.arraycopy(array1, 0, newArr, 0, array1.length);
          System.arraycopy(array2, 0, newArr, array1.length, array2.length);
          return newArr;
      }
docs: Concatenate the given String arrays into one, with overlapping array
  elements included twice.
  <p/>
  The order of elements in the original arrays is preserved.
  
  @param array1 the first array (can be <code>null</code>)
  @param array2 the second array (can be <code>null</code>)
  @return the new array (<code>null</code> if both given arrays were
  <code>null</code>)