where do you declare local variables ??

[Dave Van Even]

Hi,
local variables that you need in a block, do you declare them at the top of the block, or when you need them ??
do you do
long test;
for (int i=0;i<whatEver;i++)>
{
test = ...
}
or do you do
for (int i=0;i<whatEver;i++)>
{
long test = ...
}

I know the above one is more efficient, but the below one produced more readable code... No problem if you only use one var, but there are alot of vars I use sometimes
What's your opinion ??

method

[Wilfried LAURENT]

Personaly, I prefer the second solution :

for (int i=0;i>whatEver;i++)
{
long test =...
}

for the following simple reason. In the first case, the risk is to forget to remove the variable declaration if ever you remove the loop. Moreover, I do not like scrolling back and forth to see what the variable name or type exactly was.
W.

[Cindy Glass]

If you declare a variable in a for block, the variable is local to that BLOCK and can not be referenced outside it.

<font size=2.5>
class Test  {
    public static void main(String args[]){
          for (int i=0; i<10 ; i++){
               int j = i;
          }         
    System.out.println(j);  //compile errror "undefined variable"
    }
}

So it sort of depends on what you are doing.

[Marilyn de Queiroz]

In C, you had to declare your stuff at the top of the function and initialize it later. In Java, the rule of thumb is to not declare something until you have to.

[William Barnes]

I understand declaring everything as local as possible, but if you declare something within a loop are you not slowing things down - for no real good reason?

[Dave Van Even]

That is what I was also thinking!!
It's also possible that alot of objects will gave to be created while in a loop.

[Wilfried LAURENT]

You are right. The loops (while, for, do) may not be good examples for local variable declarations inside the block they are used. But I think it can be applied for other block types (if-then, try-catch ...).
W.

[Marilyn de Queiroz]

>It's also possible that alot of objects will gave to be created while in a loop.

An int is not an object. The question changes if you are declaring objects within the loop.

Have you tried timing it both ways? I suggest that you loop a billion times with the int declared in the loop and again with the int declared outside the loop, and see if it makes a difference.
[This message has been edited by Marilyn deQueiroz (edited October 12, 2001).]

[William Barnes]

An int is not an object. The question changes if you are declaring objects within the loop.

Good point.
So I did as you suggested and the results came out opposite of what I thought they schould be. Doing everything inside of the loop is actually faster, for an int and an object. Let me know if did something wrong here.
Here are the results:
Test #1 took: 2312 // int outside of loop
Test #2 took: 2158 // int inside of loop
Test #3 took: 34 // object outside of loop
Test #4 took: 0 // object inside of loop
Dummy object:

public class dummyClass
{
    private int One ;
    private int Two ;
    private int Three ;
    
    dummyClass( int X, int Y, int Z)
    {
        One = X ;
        Two = Y ;
        Three = Z ;
    }
    public void setOne( int X) 
    {
        One = X ;
    }
}

Test driver:

public class TestDriver_loop
{
    public static void main( String [] args)
    {
        long timeStart, timeStop, timeElapsed ;
        long timeStart2, timeStop2, timeElapsed2 ;
        long timeStart3, timeStop3, timeElapsed3 ;
        long timeStart4, timeStop4, timeElapsed4 ;
        long max = 10000000 ;
        timeStart = System.currentTimeMillis() ;
        int j ;
        for( long i = 0; i < max; i++)
        {
            j = 10 ;
        }
        timeStop = System.currentTimeMillis() ;
        timeElapsed = timeStop - timeStart ;
        System.out.println("Test #1 took: " + timeElapsed) ;
        
        timeStart2 = System.currentTimeMillis() ;
        for( long i = 0; i < max; i++)
        {
            int k = 10 ;
        }
        timeStop2 = System.currentTimeMillis() ;
        timeElapsed2 = timeStop2 - timeStart2 ;
        System.out.println("Test #2 took: " + timeElapsed2) ;
        timeStart3 = System.currentTimeMillis() ;
        dummyClass dummy = new dummyClass( 1, 2, 3) ; 
        for( int i = 0; i < 100; i++)
        {
            dummy.setOne( 4) ;
        }
        timeStop3 = System.currentTimeMillis() ;
        timeElapsed3 = timeStop3 - timeStart3 ;
        System.out.println("Test #3 took: " + timeElapsed3) ;
        
        timeStart4 = System.currentTimeMillis() ;
        for( int i = 0; i < 100; i++)
        {
            dummyClass dummy2 = new dummyClass( 1, 2, 3) ; 
            dummy2.setOne( 4) ;
        }
        timeStop4 = System.currentTimeMillis() ;
        timeElapsed4 = timeStop4 - timeStart4 ;
        System.out.println("Test #4 took: " + timeElapsed4) ;
    }
}