Generics - Unboxing items in enhanced for loop

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subterfusion
Posts:11
Registered: 8/12/02

Unboxing items in enhanced for loop
Aug 18, 2003 8:57 AM

Consider the following code:

Collection<Integer> c = new ArrayList<Integer>();
c.add(1);
c.add(new Integer(2));
c.add(3);
 
for(int i : c) {
    // do something
}

Shouldn't unboxing allow me to treat each item in the Collection as a primitive int rather than the Object version?

gafter
Posts:669
Registered: 6/25/98

Re: Unboxing items in enhanced for loop
Aug 18, 2003 2:46 PM (reply 1 of 3) (In reply to original post )

Shouldn't unboxing allow me to treat each item in the
Collection as a primitive int rather than the Object
version?

Perhaps, but the current prototype implements boxing/unboxing
as an argument conversion only.

enotecha
Posts:1
Registered: 9/20/00

Re: Unboxing items in enhanced for loop
Mar 1, 2004 7:27 AM (reply 2 of 3) (In reply to #1 )

Actually that is not true. This code works fine which means that return values are unboxed:

Collection<Integer> foo = new ArrayList<Integer>();
foo.add(3);

int i = foo.get(0);

This is a bug. I'm going to open a ticket today if I have time and the bug database application doesn't crash again.

afreije
Posts:146
Registered: 11/10/98

Re: Unboxing items in enhanced for loop
Mar 1, 2004 3:05 PM (reply 3 of 3) (In reply to #1 )

please note that

for (int i: s) {
   ...
}

is not really safe because iterable s can contain null values, so you should know for sure that s contains no null values if you use this construct.
If you are not sure, ou should use something like

for (Integer i: s) if (i != null) {
   ...
}

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