Re: Integer 128 != Integer 128 ??

Daniel Pitts <>
Tue, 12 Oct 2010 20:37:08 -0700
On 10/12/2010 8:25 PM, Peter Duniho wrote:

Eric Sosman wrote:

class Whatever {
// ...
private static Integer count = 0;
static void incrementCount() {
synchronized(count) {
// ...

.... and then he found that it wasn't working properly. It's my
belief that auto-boxing was entirely responsible for this error:
without auto-boxing, the compiler would have prevented him from
making it in the first place. To put it another way, auto-boxing
silenced a compile-time error and replaced it with a hard-to-debug
run-time error; in my book that's not an improvement.

If your example was:

class Whatever {
// ...
private static int count = 0;
static void incrementCount() {
synchronized(count) {
// ...

?then it would be plausible. :) Integer is a reference type and should
not require boxing for use in the "synchronized" statement.

Its not the synchronized statement that boxing affected, its the ++
statement. count is a *different* reference every time "incrementCount"
gets called, and therefore two threads may see different values of count
inside the synchronize block. They will indeed become less likely to
properly synchronize over time.

synchronizing on a primitive is not valid, so the compiler *would* have

And yes, even in C#, locking on a value type is a very bad idea. :)


For posterity, the correct approach is to use an AtomicInteger.

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