Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!aioe.org!.POSTED!not-for-mail
From: Abu Yahya <abu_yahya@invalid.com>
Newsgroups: comp.lang.java.programmer
Subject: Class.forName().newInstance() vs new
Date: Sat, 11 Jun 2011 22:43:59 +0530
Organization: Aioe.org NNTP Server
Lines: 33
Message-ID: <it07on$ilc$1@speranza.aioe.org>
NNTP-Posting-Host: VXdcwsc5kgxY1YKHPVeYyQ.user.speranza.aioe.org
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
X-Complaints-To: abuse@aioe.org
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.17) Gecko/20110414 Thunderbird/3.1.10
X-Notice: Filtered by postfilter v. 0.8.2
Xref: x330-a1.tempe.blueboxinc.net comp.lang.java.programmer:5205

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?