Re: Class.forName().newInstance() vs new
On 06/12/2011 04:37 PM, Martin Gregorie wrote:
On Sun, 12 Jun 2011 07:10:07 -0700, Patricia Shanahan wrote:
Is there really any program that instantiates so many database managers
that the difference between newInstance and constructor, and the
pipeline reloads related to conditional branches, become measurable?
Is there actually that much difference? It strikes me that both 'new' and
Class.forName() are doing essentially the same, namely searching the
class path for the required class, loading it into the JVM and
instantiating an object from it.
Actually, the code will execute a Class.forName() under the hoods for
the version with direct instantiation. There is still a fundamental
difference though: the solution explicitly using Class.forName() will
provide the name at runtime while the version with the explicit
constructor call will have it compiled into the code. Consequently when
providing the name at runtime reflection has to be used (which is
usually a tad slower).
The conceptual difference between providing a type at compile time and
run time is reflected by the necessity to use reflection (in the dynamic
case) which defers particular type checks to runtime - which is usually
significantly slower when done frequently because it has to be done for
_every_ call.
I also wonder if 'new' might not be
implemented as a wrapper for Class.forName(). It certainly could be done
that way: both return a class object if they are successful and throw an
exception if the class can't be found.
Class.forName() only yields a class (if successful) while new SomeClass
yields an instance - so new is more like a wrapper around
Class.forName().newInstance(). But as I said, there is a fundamental
conceptual difference between the two.
Kind regards
robert