title: Best design to share class instance between many classes
body: <p>I am going to create a utility Class <code>APIUtility</code>, it wraps a unique Object token generated by the server engine, once I used my username and password to get the Object token, I get the door is opening so I can access the engine anytimes if the token is still alive.</p>
  
  <p>I want to use existing 'APIUtility' once I get the access to avoid unnecessary authentication effort. and with this 'APIUtility' I get directly call many functions to server engine. but right now, I have some else classes, they are under different place to take different responsibility: e.g. build data, logic validation, condition elevation, so these classes both need to have a base line use <code>APIUtility</code> to access engine data, do anybody have good design for this? because I fell it every class have a variable <code>APIUtility</code> we need set it for create a instance of these classes is not a good design.</p>