Integer auto-unboxing and auto-boxing gives performance issues?

Question

We are currently doing some iterations and other operations using x++; where x is an Integer and not an int.

Operations may be repeated throughout some user operations on our system but nothing too complex or numerous like a Mathematical application, maximum up to 10000 times per user transaction..

Will this unboxing and later boxing affect our performance by some noticeable milliseconds?

Answer 1

http://download.oracle.com/javase/1.5.0/docs/guide/language/autoboxing.html

"The performance of the resulting list is likely to be poor, as it boxes or unboxes on every get or set operation. It is plenty fast enough for occasional use, but it would be folly to use it in a performance critical inner loop.

So when should you use autoboxing and unboxing? Use them only when there is an “impedance mismatch” between reference types and primitives, for example, when you have to put numerical values into a collection. It is not appropriate to use autoboxing and unboxing for scientific computing, or other performance-sensitive numerical code. An Integer is not a substitute for an int; autoboxing and unboxing blur the distinction between primitive types and reference types, but they do not eliminate it."

Answer 2

Yes, there is a performance impact. The equivalent code produced for ++x involves creating a new Integer object each time. x++ additionally creates a temporary variable to store the previous integer reference, and some manipulation. You can verify this by disassembling the class file.