Create an instance of this class. Assumes that clazz has already been
initialized. Optimizes Class.newInstance() by caching and using the
no-arg Constructor directly. Class.newInstance() looks up the constructor
each time.
exception: InstantiationException - Zero arg constructor can not be executed exception: IllegalAccessException - Class or zero arg constructor is not public. exception: InvocationTargetException - Exception throw in zero-arg constructor.