code: public void ensureSpareCapacity(int n)
          throws IOException
      {
          if (_size+n>_buf.length)
          {
              if (_fixed)
                  throw new IOException("Buffer overflow: "+_buf.length);
              byte[] buf = new byte[(_buf.length+n)*4/3];
              System.arraycopy(_buf,0,buf,0,_size);
              _buf=buf;
          }
      }
docs: /* ------------------------------------------------------------