size += len;
                if (size == bufferSize) {
                    final char[] newBuf = new char[bufferSize + initialCapacity];
                    System.arraycopy(buf, 0, newBuf, 0, bufferSize);
                    buf = newBuf;
                    bufferSize += initialCapacity;
                }
            }
            return new String(buf, 0, size);