RE: Cost of instantiating

Variables and objects aren't the same thing. Creating new objects is done by 
the "new" keyword and where the variables that refer to those objects are 
declared is irrelevant (at least as far as numbers of objects created is 
concerned).

It's best to declare variables in the smallest scope possible (i.e. the second 
version). If you are going to use the first version, it would be better to 
initialize the variables to null. The code you have there creates five objects 
that are thrown away almost immediately.

And in this case, since an Integer object is immutable, you could cut down on 
the number of objects created like this:

Iterator iter = myList.iterator();
while (iter.hasNext()) {

    Integer total1 = new Integer(0);
    Integer total2 = total1;
    Integer total3 = total1;
    Integer total4 = total1;
    Integer total5 = total1;
    
    total1 = methodTotal1();
    total1 = methodTotal1();
    total1 = methodTotal1();
    total1 = methodTotal1();
    total1 = methodTotal1();    
    // write totals to PDF
}

But again, total1 is assigned the value of methodTotal1(), so whatever value it 
had before gets thrown away. Assuming that you didn't finish editing your 
posted code, an even better piece of code would be

Iterator iter = myList.iterator();
while (iter.hasNext()) {

    Integer total1 = methodTotal1();
    Integer total2 = methodTotal2();
    Integer total3 = methodTotal3();
    Integer total4 = methodTotal4();
    Integer total5 = methodTotal5();    
    // write totals to PDF
}

in which no "new Integer(0)" objects are created to be immediately thrown away.

HTH
PC2

-----Original Message-----
From: java400-l-bounces@xxxxxxxxxxxx [mailto:java400-l-bounces@xxxxxxxxxxxx] On 
Behalf Of albartell
Sent: June 16, 2005 07:52
To: 'Java Programming on and around the iSeries / AS400'
Subject: Cost of instantiating

I have been reading in different publications by well known authors about how 
we don't need to be as concerned about instantiating a few extra objects here 
and there because the processing in JDK1.5 is so much better than that of 
JDK1.3  (note that these comments have come in from the J2EE crowd).

So I have an example I would like comments on below. In one I create my objects 
outside of the while loop and in the latter one I create the variables within 
my while loop. Note that I don't need to have access to the variables outside 
my while loop, but if I declare them outside the while loop I need to 
initialize them with each loop iteration.

My question would be, do I save anything (meaning memory, CPU cycles, etc) by 
declaring my variables outside my while loop?