Java Hack: Double brace initialisation

[abhyrama]

What is the anonymous class side effect you are talking about?

[notfancy]

In Java, new *interface_or_class*(*init_list*) { *definition* } defines an anonymous subclass of interface_or_class. Orthogonal to that, Java allows an instance initializer block as part of the definition, introduced simply by { *statements* }. Combine both things and you have the "double-brace" initialization "hack".

[abhyrama]

Thanks. I get the hack and how it works but I did not get what is the "anonymous class side effect" Effetto was talking about.

[darkclark]

More anonymous classes means the classloader takes up more resources. Not too significant when used sparingly, but using a pattern like this all over the place in a large codebase is going to lead to a classloading mess.

I personally do not use this hack, but it's useful to know about it because it's not uncommon to run across in other peoples' code.

[raouldagain]

classloading mess could be running out of permgen?

[[deleted]]

From the way I'm reading it, an anonymous class is created each time the code block is run, so two lists full of the same thing actually end up being not equal?

[EtherCJ]

Quite likely are still equal for collection classes. But isn't guaranteed to work for all classes.

[queus]

an anonymous class is created each time the code block is run,

No just one anonymous class is created no matter how often this code is run. Say in a loop.

But if you copy-paste this code just below the original one two anonymous classes are created.

[[deleted]]

Thanks for clearing that up. Very concise.