! Illegal parameter number in definition of \NewValue

You should use the url and urldate, rather than howpublished and note:

\begin{filecontents*}{\jobname.bib}
@misc{jdk,
  author = {Oracle},
  title = {Platform, Standard Edition 7 Development Kit},
  url = {http://www.oracle.com/technetwork/java/javase/jdk-7-readme-429198.html#contents},
  urldate = {2015},
}
\end{filecontents*}

\documentclass{article}

\usepackage[backend=bibtex]{biblatex}

\DefineBibliographyStrings{english}{%
  urlseen={Accessed:}% %%% not `visited on'
}

\addbibresource{\jobname.bib}

\begin{document}

Hello world\cite{einstein} I do not if it \cite{jdk} will work test
\nocite{Doe:2009:Online}

\printbibliography

\end{document}

Note that the filecontents* environment is just to make the example self contained and you can use your file (after modifying it as suggested).