Re: Class.forName().newInstance() vs new

From:

Abu Yahya <abu_yahya@invalid.com>

Newsgroups:

comp.lang.java.programmer

Date:

Sat, 11 Jun 2011 23:53:45 +0530

Message-ID:

<it0brg$s3t$2@speranza.aioe.org>

On 6/11/2011 11:19 PM, Robert Klemme wrote:

On 11.06.2011 19:13, Abu Yahya wrote:

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? What is the best approach to instantiate classes
whose type you don't know at compile time?

I would stick with the forName() approach. If performance is critical
then I would define an interface for the factory method and configure
the name of a class which much implement this interface. Then you need
forName() only once (for instantiating the factory instance) and can use
new in factory methods (or do even more fancy things like caching etc.).

Thanks for your reply, Robert.

Could you give an example of how the factory method might look like?

Thanks in advance!

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