StringBuilder performance boost

[Alvari-Kupari]

Refactored ParserUtil to use a stringbuilder when concatenating a string within a loop to boost performance. Also added miussing override annotations to align with codestyle conventions

[sim-wangyan]

Thanks for the pull request! Could you minimize it?

[Alvari-Kupari]

My apologies, I had an automatic code formatter which made the diff file include unnecessary changes. I've repushed the changes without formatting to include only the key changes.