code: public char[] asCharArray()
      {
          int n = getIndexCount();
          if (getIndexSize() != 2)
          {
              throw new UnsupportedOperationException("Cannot convert int indices to char array");
          }
          if (n <= 0)
          {
              return null;
          }
          return NativeIndexBuffer.getShortArray(getNative());
      }
docs: Get the triangle vertex indices of the mesh as a char array.
  <p>
  The indices for each
  triangle are represented as a packed {@code char} triplet, where
  {@code t0} is the first triangle, {@code t1} is the second, etc.:
  <p>
  <code>
  { t0[0], t0[1], t0[2], t1[0], t1[1], t1[2], ...}
  </code>
  <p>
  Face indices may also be {@code int}. If you have specified
  char indices, this function will throw an exception.
  @return char array with the packed triangle index data.
  @see #asIntArray()
  @throws IllegalArgumentException if index buffer is not <i>char</i>