code: public static int[] insert(int[] array, int currentSize, int index, int element) {
          assert currentSize <= array.length;
  
          if (currentSize + 1 <= array.length) {
              System.arraycopy(array, index, array, index + 1, currentSize - index);
              array[index] = element;
              return array;
          }
  
          int[] newArray = new int[growSize(currentSize)];
          System.arraycopy(array, 0, newArray, 0, index);
          newArray[index] = element;
          System.arraycopy(array, index, newArray, index + 1, array.length - index);
          return newArray;
      }
docs: Primitive int version of {@link #insert(Object[], int, int, Object)}.