When iterating over an array using an indexed loop, you typically
need to access the element, as follows:
for(int i=0;i<100;i++) {
String s = array[i];
...
}
Java performs bounds checking on the array[i] access to make sure i
is within the limits of the array. Granted, there are optimizations
the JVM can do in many cases using escape processing to know that i
will always be in the range, but it is not always feasible.
when you use
for(String s : array) {
}
the JVM uses its own internal indexer that it knows cannot be outside
the bounds, and thus the bounds checking can be avoided.
I would need to read the spec to know what happens if the array
changes during the loop execution - my bet is that the loop maintains
a reference to the original array, and thus it continues to work.
On Apr 11, 2008, at 2:28 AM, Endre Stølsvik wrote:
robert engels wrote:
The 'foreach' should be faster in the general case for arrays as
the bounds checking can be avoided.
Why is that? Where do you mean that the bounds-checking can be
avoided?
But, I doubt the speed difference is going to matter much either
way, and eventually the JVM impl will converge to near equal
performance.
This I actually agree on: if the foreach has some disadvantage of
explicit indexing through an array, it will at some point be fixed
so that it doesn't have this disadvantage anymore..
Endre.
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