code: public BigInteger getBigInteger (int index) throws JSONException {
          Object object = this.get(index);
          BigInteger val = JSONObject.objectToBigInteger(object, null);
          if(val == null) {
              throw new JSONException("JSONArray[" + index +
                      "] could not convert to BigDecimal ("+ object + ").");
          }
          return val;
      }
docs: Get the BigInteger value associated with an index.
  
  @param index
  The index must be between 0 and length() - 1.
  @return The value.
  @throws JSONException
  If the key is not found or if the value cannot be converted
  to a BigInteger.