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Wednesday, April 8, 2026

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00:36:56pr3d4t0r:: yawn ::
00:36:59pr3d4t0rGood morning.
00:37:10pr3d4t0rdreamreal!! Come to #cime or the other channel when you have a moment?
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12:52:38* CodeGeek!~codegeek@about/java/CodeGeek changed the topic to: Welcome! || Read Channel Rules at https://javachannel.org/ before participating. || Paste limit is two lines; ~pastebin lists options. || No applets, please. || Minecraft, Android, and Javascript all have their own channel. || You are being logged.
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13:08:06* CodeGeek!~codegeek@about/java/CodeGeek changed the topic to: Welcome! || Read Channel Rules at https://javachannel.org/ before participating. || Paste limit is two lines; ~pastebin lists options. || No applets, please. || Minecraft, Android, and Javascript all have their own channel. || You are being logged.
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14:06:41dreamrealaaaaand nevet should be back. Still finding transaction leaks. :/
14:06:51dreamrealstill muted HERE, though. :D
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18:55:20dreamrealhttps://bytecode.news/posts/2026/04/boilerplate-three-ways
18:55:20javabotdreamreal's title: "Boilerplate Three Ways | bytecode.news"
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20:45:34mawkhi
20:45:56mawkis this calling 'new' under the hood? byte[] a = {1, 2, 3};
20:46:18mawki.e. is this equivalent to byte[] a = new byte[3]; a[0] = 1; a[1] = 2; a[2] = 3;
20:46:29DoofusCanadensisdoubt it
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20:46:53DoofusCanadensisbyte != Byte
20:46:56mawkI'm writing JavaCard and need to avoid 'new' as much as possible
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20:50:43jbosmansif implementation details like that matter a lot i'd suggest investigating how to validate answers to such questions, i'm thinking it'll lead to reading bytecode (aka jvm assembly)
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20:51:31jbosmanswhich i never do because i don't work at that level of detail
20:52:07Chronosmawk: Yes, as far as I know, it's identical to: byte[] a = new byte[]{1, 2, 3};
20:52:12ChronosSo I believe it does indeed call "new".
20:52:16Chronos(Corrections welcome.)
20:52:45ernimrilChronos, compile it and then check with javap
20:53:26ChronosIn Java, every array is a full-fledged object.
20:55:43mawkhmmm
20:55:48jbosmanswhat ernimril said
20:55:49mawkthanks
20:57:14sonOfRamawk: byte[] a = {1, 2, 3};
20:57:16sonOfRaoops
20:57:21sonOfRamawk: https://javap.yawk.at/#lnBjVV
20:57:22nevetjavap pastebin
21:02:49jbosmansalso, https://godbolt.org ftw
21:02:50nevetCompiler Explorer
21:04:01sonOfRatrue, but javap.yawk.at is made by (former) channel regular yawkat!
21:04:49jbosmanskudos for that ^
21:05:34mawkah yes indeed sonOfRa , thanks!
21:05:47jbosmansas far as i can see creating a new array doesn't create a new object
21:06:19jbosmansstatic int[] square() { return new int[]{9999}; }
21:06:24ernimriljbosmans, what about the newarray ?
21:06:29jbosmans 0: iconst_1
21:06:29jbosmans 1: newarray int
21:06:29jbosmans 3: dup
21:06:29jbosmans 4: iconst_0
21:06:29jbosmans 5: sipush 9999
21:06:32mawkwell it calls "newarray byte" so it must be allocating it on the heap
21:06:52mawkso I should do that only in the constructor of my applet so it's only called once
21:07:05mawkI can technically trigger the garbage collector but it has to be done manually and it's not portable, not every card has it
21:08:01jbosmansthanks for unbanning :)
21:10:35jbosmansmawk, there's the epsilon gc which doesn't do anything iirc, might be useful for measuring/.. to accomplish your goals
21:11:01mawkah yeah, I can run this on a simulator on a pc
21:11:08jbosmansshould you want to invest in that approach
21:20:05mawkthanks
21:21:09jbosmansmawk, assuming sarcasm, understand what you mean (i think). You could make it runnable on a pc if you can separate the dependencies from the code that's actually doing the work (or the work you care about)
21:21:23jbosmansoverlapping msgs:)
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21:35:17jreichermawk: are you really assigning the byte array something known at compile time? Or is that just how you wrote the example?
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21:52:14mawkyes it's known at compile time
21:52:40mawkmaybe if I set it as "final" it won't make an allocation
21:54:31jbosmansafaik object instantiations are extremely cheap on jvm
21:55:11ernimrilit is on all modern jvms, yes, has been so for a long time. Also constants are quite often inlined by the compiler
21:55:36jbosmans~jep 519
21:55:37javabot'JEP 519: Compact Object Headers' can be found at http://openjdk.java.net/jeps/519
21:55:39nevetJEP 519: Compact Object Headers
21:56:02jbosmansalso, it was pretty cheap before, too
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21:58:44jbosmans(before java 25)
22:00:44jbosmansalso, up to recently, i compiled some tools using docker to an ubuntu 18/debian 10 compatible binary
22:01:01jbosmanswhich really made a difference for cmdline tools
22:02:44jbosmansfwiw it was compatible by compiling in dedicated docker containers, i just upgraded the container OS versions
22:03:27jbosmansiirc i got java+spring+jdbc+postgres+code down to ~60mb, which was nice
22:03:56jreichermawk: if it's known at compile time then declare it static and don't worry about the new. At worst it will only be done once, but perhaps not at all.
22:03:59jbosmansUPX compression could drive that down substantially, but that would take longer to execute (because of decompression)
22:04:17jreicherA good rule of thumb IMO is to always tell the compiler everything you know.
22:07:08mawkjbosmans: this is running on a smartcard, it's a a very small and slow microcontroller
22:07:20mawkwith just a couple hundred bytes of RAM to spare, maybe a thousand
22:07:46jbosmansmawk, great to be working on that :-)
22:07:58jbosmansi actually recognized JavaCard
22:07:59jreicherIs it possible Java is not the best language for that kind of target? (Honest question; I have no experience in this area)
22:08:28mawkwell there's no choice, java is all they run; in your credit card, your epassport, your SIM card
22:08:41mawkyou can sometimes run C but you need to sell your soul for a NDA
22:08:51jbosmansmawk, which context? eid or alike?
22:09:05mawkI'm working on a PKI smartcard
22:09:38jbosmanssweet, iirc our eid runs JavaCard too
22:09:49mawkjava is actually a sane choice for the application, the JVM is fully controlled by the OS and can apply all the static checks and security mitigations they want
22:09:50jbosmanscrazy stuff
22:10:46mawkthey can do stuff like rolling back transactions in case of tearing, skewing the clock inbetween instructions or running instructions several times to throw off side channel attacks; and also exceptions are an integral part of how the card communicates with the reader, that's how you set the APDU status codes
22:11:45jbosmansmawk, what jdk version are you working in?
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22:15:32mawkit's javacard 3.0.5
22:15:34mawkcompiling with jdk 17
22:18:33jbosmansthat's not too bad for such a restricted context
22:19:14jbosmansiirc records are already supported
22:19:41jbosmansbest use those wherever they make sense
22:20:12jbosmansbecause both the compiler and jvm will know they're mean to be (shallowly) immutable
22:21:17jbosmansalas way post midnight, sweet dreams
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22:57:49dreamrealfor javacard, eh
22:57:54dreamrealThat's a little surprising
23:04:56mawkwhy?
23:07:06dreamrealjavacard's not very common in the wild. What are you deploying it to?
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23:34:34mawkI'm currently trying to add remote management capabilities with public key crypto
23:34:39mawklike SIM cards have
23:35:04mawkthen you can open a secure channel with the card even through an untrusted network
23:35:36mawkthen the card will serve as a secure element to hold keys for mTLS or other things, in an embedded product, in SIM format
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23:38:32mawkand it's running on a JCOP 4 smartcard from NXP
23:45:50dreamreal*nod* nice!
23:49:11mawkI have half of the secure channel thing working, I can request AES session keys from the card and then continue with AES and CMAC
23:49:35mawkbut now I need to wrap the AES keys with a public key instead of transmitting them in cleartext
23:50:25dreamrealso I have VERY VERY VERY little experience with that profile, but in general you avoid allocations like the plague: new is fine *but* you reuse *everything* you can, so if you allocate an array, you reuse that array for the lifetime of the application
23:50:49mawkyeah indeed
23:51:08dreamrealIt's like you're writing in MUMPS except with java syntax, wooo
23:51:35mawkI can request transient arrays which get cleared either on deselect or on reset (like if the application is selected several times on different logical channels or different interfaces like contact vs contactless)
23:51:42mawkbut then it's not with new
23:52:00dreamrealI don't know if there's a GC on that profile at all: you'd want to allocate and preserve
23:53:47dreamrealunless things have changed! Like I said, I've got VERY little experience here, like "ooo I tried it once"
23:54:55mawkyeah some cards do have a GC but not all of them
23:55:06mawksome cards even have ints and not just bytes and shorts
23:55:10mawkluxurious
23:55:31mawkand you need to invoke the GC manually, and it will maybe run next time a command is received
23:55:39dreamrealI think I last did javacard on a lark for javaone 2007? maybe 2008?
23:56:06mawkah yeah the standards were quite different then
23:56:36mawkI think the standard was still to use the VISA platform manager instead of being the globalplatform thing of now
23:57:12dreamrealGosh, I don't remember that at all - we had this physical connection to the board, I don't even remember what it was called to install the application
23:57:42dreamrealI remember having a GPS available, which I thought was going to be great for basically building the apple tags using java
23:58:17dreamreallike how train car locators work: when connected to an open network, send an identifier ("package XYZ is at X:Y at 23:01")