Re: Class.forName().newInstance() vs new
Abu Yahya <abu_yahya@invalid.com> wrote in news:it07on$ilc$1
@speranza.aioe.org:
I have a class that instantiates a private member based on a value in a
configuration file.
The value is used to determine the class name.
I initially decided to use code similar to the following:
// class name comes from property file
String dbMgrClassName = props.getProperty("db.manager");
Class<?> k = Class.forName(dbMgrClassName);
db = (DB) k.newInstance();
db.init(props);
However, a colleague pointed out that using "new" is faster than using
"Class.forName().newInstance()". So, I changed the code to the following:
String dbMgrClassName = props.getProperty("db.manager");
if (dbMgrClassName.equals("DB2"))
db = new DB2();
else if (dbMgrClassName.equals("Oracle"))
db = new Oracle();
else if (dbMgrClassName.equals("SQLServer"))
db = new SQLServer();
else { // handle unrecognized
Class<?> k = Class.forName(dbMgrClassName);
db = (DB) k.newInstance();
}
db.init(props);
My question is: Does using if-else statements like the above really
improve performance?
Maybe yes, maybe no. If you don't have a benchmark that shows it to be an
issue, don't worry about it. Initializing the databas manager is probably
going to be a lot more preformance-consuming than anything else that you
are doing here.
What is the best approach to instantiate classes
whose type you don't know at compile time?
Well, actually you _do_ know the type for db, you just didn't show us
directly; apparently it is DB. What you don't know at compile time is the
implementation.
I prefer to use java.util.ServiceLoader myself. It means that you have to
have "a provider-configuration file in the resource directory META-
INF/services" instead of a property or a value in a separate configuration
file. This could be a good thing or a bad thing, depending upon your
application.