title: Convert string to valid Java variable name
body: <p>For a code generation tool I'm working on, I need to take a string and generate a valid java variable name from it, but I'm not sure about the best way to do it.</p>
  
  <p>For example:</p>
  
  <p><code>"123 this is some message !"</code> => <code>_123_this_is_some_message</code> ( or something similar) </p>
  
  <p>Thanks</p>