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| welldone |
in tomcat, I want to redirect incoming HTTP connections to HTTPS, can I have 2 <Connectors> server.xml and use redirect parameter? |
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| _lucifer |
tech support |
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| _lucifer |
welldone, Hello, ##java is not a technical support channel for your Java apps or virtual machines; it's a development channel for enthusiasts to discuss programming with the Java language. Please ask the vendor of your software for support if you're having trouble with it. |
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| mgd |
I'm about to ask a stupid question so please bear with me as I'm not sure how to put this. How does Java define a method and a function? |
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| mgd |
Is everything ultimately a method or does java.util.function actually provide functions through streams and lamdas? |
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| [twisti] |
mgd: you need to elaborate what aspect your question is about. how its defined in the JLS ? how it looks in the bytecode ? whats legal ? |
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| [twisti] |
ah. ju.function is nothing but a marker interface, it doesnt really do anything on its own at all |
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| [twisti] |
wait, brain hiccup |
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| _lucifer |
i think you meant FunctionalInterface |
[06:08]
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| [twisti] |
do you mean java.util.function.Function, or the package ? |
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| mgd |
the package |
[06:09]
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| [twisti] |
or, as _lucifer said, the FunctionalInterface ? |
[06:09]
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| [twisti] |
ah. the package just defines convenience interfaces, really |
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| [twisti] |
you could redefine your own if you wanted to |
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| mgd |
I'm a little lost as I've seen the terms method and function used interchangeable. I guess I just want to know how Java defines those two terms |
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| _lucifer |
everything is a method in java. you cannot have top level functions. |
[06:10]
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| _lucifer |
not everything everything. i mean java only has methods |
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| mgd |
Sorry and a top level function is like a higher order function or have I got that wrong? |
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| [twisti] |
i think the general consensus is that if its part of a class definition, people call it a method, and if its passed around, they call it a function |
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| mgd |
@twisti so like a lambda which can be passed around |
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| [twisti] |
a top level function would be one available without a class or interface, which some languages allow, but java doesnt |
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| _lucifer |
like in some languages say Python, you can define a function outside a class. |
[06:12]
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| _lucifer |
^^ |
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| mgd |
Ok, so since every action in Java has to be linked to a class/interface, statically or otherwise, they are all methods? |
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| _lucifer |
not sure what you aiming at here, but IMO for all practical purposes you can use the the term methods and functions interchangeably. |
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| mgd |
It's a little hazy for me still. I can't really find a solid definition of a function and method which is separate to a particular language or paradigm. |
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| [twisti] |
there is no such thing |
[06:17]
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| [twisti] |
language is a fluid and imprecise thing, people use terms differently and sometimes they evolve over time |
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| mgd |
So it's just down to the vocabulary that the language uses? |
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| Maldivia |
mgd: it's actually straight forwards, java doesn't have functions, it only has methods :D |
[06:18]
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| mgd |
@Maldivia I can live with that :) |
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| [twisti] |
yes. if you want rock solid definitions applicable to java 100%, check out the Java Language Specification (JLS) |
[06:18]
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| Maldivia |
"A method declares executable code that can be invoked, passing a fixed number of values as arguments." |
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| mgd |
That's really useful. I've never really looked into the JLS |
[06:21]
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| Maldivia |
jls |
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| Maldivia |
Maldivia, jls is short for the 'Java Language Specification'; it is the official spec that defines what java (the language) is. You can find it at https://docs.oracle.com/javase/specs/ - you can also find the 'Java Virtual Machine Specification' there, which defines java (the virtual machine). |
[06:21]
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| [twisti] |
the JLS is horribly dry at times, but actually quite readable by a layman imo |
[06:22]
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| Maldivia |
and very verbose covering 99.9% of cornercases |
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| Maldivia |
(which is good) |
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| yawkat |
how do you use logback with native-image? initializing it at build time works fine, except for file appenders, because obv it should only open the log file at runtime |
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| [twisti] |
i think today is the first time in my life that i have unironically used the (logical) XOR operator in java |
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| yawkat |
logical = on boolean? |
[06:42]
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| [twisti] |
yes |
[06:42]
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| yawkat |
imo != is usually more readable |
[06:42]
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| [twisti] |
obviously i have used XOR on bits when i played with that kind of low level stuff |
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| [twisti] |
(im writing code that deals with file ownership, and it has both an ignore list as well as a list of patterns it will handle, and the code needs to be able to answer whether it deals with a file, and of course both dealing with it AND ignoring it is just as wrong as doing neither) |
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| [twisti] |
!= didnt feel apropriate for saying 'either/or' |
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| [twisti] |
of course, i just realized that something being both ignored and covered, that really ought to throw an exception, not just return false |
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| [twisti] |
bye bye, ^ use |
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| solvr |
My usual strategy with constructors is to consider them a low level "everything and the kitchen sink" collectors of initial configuration and state, and relegate the nice UX to factory methods and builders. How does that match common practices. |
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| _lucifer |
if you want control over object creation, prefer builders or factories otherwise constructors are fine i think. |
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| _lucifer |
effective java covers this is some detail iirc. |
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| solvr |
_lucifer, my point was I usually tried to keep constructors clean. Nowadays a constructor might have 10-20 arguments and I consider it OK because you rarely need to type that directly. |
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| _lucifer |
having a large number of arguments is another point in favour of builders. |
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| solvr |
_lucifer, do you have a strategy for separating "dependency injection" arguments from "object configuration" arguments. |
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| _lucifer |
I haven't had to deal with that myself yet but I'd go ahead with whatever the idiom is for that framework. |
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| solvr |
My question doesn't regard a given framework, more like 1) set of arguments where you take in dependencies from the environment (db connections, whatever) 2) set of arguments that define the object's behavior |
[07:31]
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| solvr |
Arguably those are the same things, but |
[07:31]
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| solvr |
Let's say the first set tends to be more uniform across a set of instances |
[07:31]
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| solvr |
The latter more specific |
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| _lucifer |
I am not sure I understand you correctly but all of the arguments will need to go into the constructor, only thing you can control is the order, order them as you wish but consistently. |
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| solvr |
_lucifer, I'll give an example. You instantiate factory with DB connection, logger, and few other things like that. Then you can use this factory and instantiate concrete objects by passing few extra args, implicitly the object receives everything you gave the factory as well |
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| solvr |
_lucifer, call it curried construction :P |
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| _lucifer |
sounds like AbstractFactory pattern? |
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| solvr |
_lucifer it's like an abstract factory in that you can configure a library and pass it around to make object. But it's unlike it in that the factory doesn't have to be polymorphic (it differs in construction arguments, not concrete class) |
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| solvr |
_lucifer, or maybe I misunderstand the pattern dunno |
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| solvr |
Looks like we're averaging about one "why OOP sucks" presentation per three months. |
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| wedr |
Maybe Java can be rewritten to be a data-oriented programming language? |
[08:56]
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| solvr |
Pretty much is. |
[08:57]
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| solvr |
But once per 3 months is nothing. We probably get "why cute puppies suck" presentation more often than this. |
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| sbalmos |
cute kittens are just juvenile terrorists |
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| solvr |
sbalmos, I agree, unfortunately puppies get all the hate, while they do all the work |
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| [twisti] |
can LocalDateTime.parse be coerced to accept a DateTimeFormatter that does not include a time (and substitute zeroes) ? it seems awkward to have to have two code branches for user submitted date/time patterns |
[10:18]
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| _lucifer |
something like this https://stackoverflow.com/a/34793685/5557184 ? |
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| _lucifer |
_lucifer's title: "java - Is there a way to determine if a DateTimeFormatter is date only or time only after construction? - Stack Overflow" |
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| [twisti] |
thanks, totally wrong question, but the answer still solves my problem :D |
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| mitch0 |
hm, that's pretty nice actually |
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| solvr |
Do we have some middle-ground between referencing an object directly, and using SQL-style PK/FK to reference it. |
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| mitch0 |
solvr: ? |
[11:21]
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| solvr |
Sounds weird right |
[11:21]
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| mitch0 |
Map<String, YourObject> ? |
[11:22]
|
| solvr |
mitch0, thanks |
[11:23]
|
| cheeser |
omg |
[11:24]
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| mitch0 |
cheeser: :) |
[11:30]
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| solvr |
mitch0, cheeser, ok honestly that wasn't what I needed, but I didn't want to be an asshole |
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[11:36]
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| solvr |
My problem is that I index a set of records on some criteria. Then I run a query using the index. First criteria with index, fine. But then I have a subset of records. I can no longer use my indexes on the SUBSET of records. Not efficiently at least. |
[11:36]
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| solvr |
Because the indexes are on all records |
[11:36]
|
| solvr |
I guess I'm asking is there an algorithm to efficiently compute indexes on subset of data, where the full set of data is indexed |
[11:37]
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| freeone3000 |
you want a relational database. |
[11:37]
|
| solvr |
Well, I want specifically to learn about index on subsets |
[11:37]
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| ernimril |
solvr, what does index on subset mean to you? |
[11:37]
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| solvr |
ernimril, let's say you have 1000 users. An you have a Map<userEmail, userArrayIndex> |
[11:38]
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| solvr |
ernimril, I have another similar index, on name. I get all users named John. Now I want to get all users John with email "foo@bar.baz" |
[11:39]
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| freeone3000 |
one of those is going to be a hashscan. |
[11:39]
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| solvr |
I can no longer use my index over the 1000 users, I have a subset of users John |
[11:39]
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| solvr |
freeone3000 and the other one? |
[11:40]
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| freeone3000 |
solvr: the other one uses the index, obviously. |
[11:40]
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| solvr |
Wait. |
[11:40]
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| ernimril |
yeah, with the tiny collections mentioned here it is probably not worth optimizing, but other than that I would suggest a spatial index, possibly my prtree |
[11:40]
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| freeone3000 |
solvr: you could also create a new index on email*name. |
[11:40]
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| solvr |
ernimril, I'll check this out thanks |
[11:41]
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| solvr |
freeone3000, am I misunderstanding what a "hashscan" is |
[11:41]
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| solvr |
It's not a scan... on hash? |
[11:41]
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| freeone3000 |
it is. it's the fallback method for a sql database, where each row is essentially checked for equality in linear time. |
[11:42]
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| solvr |
Oh so a linear scan |
[11:42]
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| solvr |
filter() basically |
[11:42]
|
| solvr |
Why is it called a hashscan? |
[11:42]
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| freeone3000 |
'cause it scans. on the hash. |
[11:42]
|
| solvr |
I associated it with hashtable |
[11:42]
|
| solvr |
OK |
[11:42]
|
| solvr |
Got it |
[11:42]
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| freeone3000 |
(it's going to be referenced more than once in a query, so what usually happens is a hashtable is *created* for this query alone, so you don't lose out on the work it already did when you need to do a where, or a subquery scan, or etc later) |
[11:43]
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| freeone3000 |
don't pay too much attention to me, though, I've only worked on an sql database for a *bit*. |
[11:43]
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| sonOfRa |
You can always... create a multi-column index. They're more efficient on most DBMS if you are searching on a "leftmost prefix" of the index |
[11:44]
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| solvr |
Why say that. I'm listening :P |
[11:44]
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| solvr |
sonOfRa, I'm trying to figure out the usecases where I don't know the exact column combos in advance, but I agree it's useful |
[11:45]
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[11:45]
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| sonOfRa |
Ah so basically you have... some kind of document, which you need to store and query? |
[11:45]
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| sonOfRa |
this is veering rather off-topic for this channel |
[11:46]
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| solvr |
I have collections I, basically "join" SQL style. In memory. But without SQL DB |
[11:46]
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| solvr |
OK |
[11:46]
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| solvr |
You know one of the reasons I'm trying this is figuring out how to use immutable Java records in bigger structures, without rigidly connecting them explicitly with hard references |
[11:47]
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| solvr |
A record is immutable. But the relationship, I wish, was "externalized" and mutable. |
[11:48]
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| freeone3000 |
you want a database. |
[11:48]
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| solvr |
freeone3000, well. Like a very specialized, in-memory database. If you will. |
[11:48]
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| cheeser |
h2 then |
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[11:48]
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| Diablo-D3 |
really nothing wrong with h2, it works well |
[11:49]
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| solvr |
freeone3000, more specifically all I care about is quick joins. Nothing else. |
[11:49]
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| solvr |
I'll check h2 |
[11:49]
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| solvr |
The documentation has Windows XP screenshots. Exciting. |
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[11:53]
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| solvr |
OK can I take a step back. |
[11:53]
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| solvr |
Let's forget databases, FKs and so on. |
[11:53]
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| solvr |
Let's just assume I want bunch of immutable Java records to have 1:1 or 1:N relationships. But despite the records are immutable, I want those relationships to be mutable, so I can swap a record for another record value in a given relationship |
[11:54]
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| freeone3000 |
solvr: have you considered a database? that'd be the first thing I reach for here. |
[11:54]
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| solvr |
They already come from a database. But they're a tiny subset of the database |
[11:55]
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| sonOfRa |
So query better? |
[11:55]
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| freeone3000 |
*use the database* |
[11:55]
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| solvr |
I'm not trying to filter out records. |
[11:55]
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| solvr |
I'm trying to relate them |
[11:55]
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| freeone3000 |
it also does that! that's the first word! |
[11:55]
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| solvr |
Filtering out is kind of instrumental |
[11:55]
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| solvr |
Come on, a DB returns flat records list |
[11:56]
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| freeone3000 |
no, it returns a *square* records *table* |
[11:56]
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| solvr |
Great |
[11:56]
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[11:56]
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| solvr |
That can't efficiently represent 1:N relationship |
[11:56]
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| freeone3000 |
yes, it can; that's an fk relationship, directly. |
[11:57]
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| solvr |
I don't know why I have to dumb this down so much. |
[11:57]
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| freeone3000 |
because you're bad at explaining. |
[11:57]
|
| solvr |
Fine. |
[11:57]
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| solvr |
We have a table of users, who have friends. Graph of friends. |
[11:58]
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| solvr |
What query would fetch a graph for a subset of users |
[11:58]
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| solvr |
None. You'll get a subset of users, but not in a graph |
[11:58]
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| solvr |
Rather, in a list. |
[11:58]
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| freeone3000 |
ah, okay. you're thinking as if the representation of the data and the data have to be isomorphic. |
[11:59]
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| solvr |
So now you need to materialize this relationship somehow |
[11:59]
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| solvr |
freeone3000, I don't need it to be isomorphic directly from the DB. But I somehow need to get there at some point |
[11:59]
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| freeone3000 |
so just... trace the relations. the graph exists, in the db, as relations. |
[11:59]
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| solvr |
So I trace it. |
[12:00]
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| solvr |
I build the graph say |
[12:00]
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| freeone3000 |
why are you building a graph, when the graph is already built? |
[12:00]
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| freeone3000 |
the graph is *implicit* in your data. |
[12:00]
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| solvr |
.Implicit is great, until you gotta walk it |
[12:00]
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| solvr |
Then it's not great |
[12:01]
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| Cuckoo` |
i'm very confused by this conversation, i feel like you're doing that thing where you're inventing problems that don't exist for yourself or something along those lines |
[12:01]
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| Cuckoo` |
I'm not sure i follow your description of your database schema and what you're trying to do, but usually the answer to maintaining complex relationships in java objects is just a map of some kind based on your query, but without knowing what you're trying to do and your schema, we can't write your query for you |
[12:02]
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| ernimril |
a part of the problem is that solvr never wants to actually explain what he is trying to do or why it is all high level abstract stuff |
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[12:04]
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| Cuckoo` |
It can get kind of ugly nesting maps of maps and things, but i've done it many times and it works fine if you think it through. maybe some of the more experienced people here have better more technical recommendations but in my experience it works for me |
[12:04]
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| solvr |
Let's take this "implicit graph" of friends. |
[12:05]
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[12:05]
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| solvr |
How do I provide a nice API on top of it, so people can walk it, "user foo, their friends, their friends' friends"... |
[12:05]
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| Cuckoo` |
Is this "graph" a column in a database? some code generated based on data in the database? what is this 'graph' |
[12:05]
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| solvr |
Cuckoo`, a graph of people, like on Facebook. |
[12:05]
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| solvr |
People who know each other. |
[12:06]
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| ernimril |
solvr, easy, implement something for the first 5 levels, then return everyone... six-degrees |
[12:06]
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| Cuckoo` |
sounds more like a tree |
[12:06]
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[12:06]
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| gambl0re |
how do i remove and return the removed element from a set? |
[12:07]
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| solvr |
Cuckoo`, well, a tree is a graph. |
[12:07]
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| Cuckoo` |
i don't make graphs |
[12:07]
|
| solvr |
Great |
[12:07]
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| Cuckoo` |
i use reporting tools to turn data into graphs, if i ever do that |
[12:07]
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| mbooth |
Cuckoo`: A graph has nodes (people) and edges (relationships) |
[12:08]
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| gambl0re |
you guys doing leetcode? |
[12:08]
|
| gambl0re |
interesting.. |
[12:08]
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| mbooth |
It sounds like each person record has a list of other people with which they have a relationship, hence the "implicit" nature of the graph |
[12:09]
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| _lucifer |
gambl0re: what does that mean? you are removing the element, just return it? |
[12:09]
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| Cuckoo` |
Map<User, Collection<User>> thisUserToAllFriendsMap |
[12:09]
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[12:09]
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| Cuckoo` |
build from map |
[12:10]
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| gambl0re |
_lucifer: remove returns a boolean, not the value |
[12:10]
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| rajrajraj |
i wanted to talk about oracle vs google, but i am banned in #java-talk |
[12:10]
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| _lucifer |
gambl0re: but you pass the value you want to remove to it |
[12:10]
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| mbooth |
rajrajraj: A programming channel is not really the place to discuss a lawsuit either, IMO |
[12:10]
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| gambl0re |
im removing by index |
[12:11]
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| rajrajraj |
mbooth: #java-talk is much more of a casual channeel |
[12:11]
|
| mbooth looks around |
[12:11]
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| mbooth |
rajrajraj: We are not in #java-talk |
[12:11]
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[12:11]
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| solvr |
Well there are programming implications of that lawsuit |
[12:11]
|
| solvr |
Can't we have like QA rule that the lawsuit talk stops when someone asks a Java question |
[12:12]
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| rajrajraj |
mbooth: yes i am banned there i dont even remember why |
[12:12]
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| _lucifer |
gambl0re: didn't you say you were using a Set? |
[12:12]
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| solvr |
But permit it otherwise |
[12:12]
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[12:12]
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| mbooth |
rajrajraj: Okay? |
[12:12]
|
| gambl0re |
_lucifer: ya |
[12:12]
|
| gambl0re |
i dont want dupe values... |
[12:12]
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| solvr |
rajrajraj, try #programming. The lawsuit has broad implications |
[12:12]
|
| solvr |
rajrajraj sorry ##programming |
[12:12]
|
| _lucifer |
sets are unordered |
[12:12]
|
| rajrajraj |
same banned solvr |
[12:13]
|
| solvr |
Hehe |
[12:13]
|
| rajrajraj |
proabbaly they dont like irccloud |
[12:13]
|
| gambl0re |
should i use arraylist? |
[12:13]
|
| solvr |
rajrajraj, is your nick registered, that may be it |
[12:13]
|
| rajrajraj |
its registered |
[12:13]
|
| solvr |
rajrajraj try webchat.freenode.net |
[12:13]
|
| rajrajraj |
that reveals my IP :x |
[12:13]
|
| solvr |
Oh no, your IP. |
[12:14]
|
| solvr |
P /s |
[12:14]
|
| _lucifer |
gambl0re: if you don't want duplicates, sure use set. but why are you removing by index? |
[12:14]
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| mbooth |
Hahaha, "everywhere I go I get banned -- the problem must be my client and definitely not me" |
[12:14]
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| gambl0re |
rajrajraj: you can use Tor |
[12:14]
|
| _lucifer |
which set implementation are you using? |
[12:14]
|
| gambl0re |
HashSet |
[12:14]
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| rajrajraj |
gambl0re: i am on office pc, installing tor on this is red alert :D |
[12:14]
|
| rajrajraj |
btw i just heard that spring boot is getting old |
[12:15]
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[12:15]
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| _lucifer |
gambl0re, so where do you see a method to remove by index? |
[12:15]
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| rajrajraj |
is there something advanced in spring boot |
[12:16]
|
| gambl0re |
_lucifer: what do you mean? |
[12:16]
|
| gambl0re |
set.remove(index_pos) |
[12:16]
|
| _lucifer |
check the javadoc, there is no such method. |
[12:17]
|
| gambl0re |
im using intellij, the remove method is being shown |
[12:17]
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| mbooth |
gambl0re: Are you *sure* it's a Set then? |
[12:18]
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| _lucifer |
well, its the remove(Object) method |
[12:18]
|
| gambl0re |
im doing Set<Integer> nums = new HashSet<>(); |
[12:18]
|
| gambl0re |
isnt that a set? |
[12:18]
|
| _lucifer |
yes, but it will remove the integer you pass to it. |
[12:19]
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| mbooth |
Yes, but it has remove(Object) and NOT remove(index) |
[12:19]
|
| mbooth |
You should actually read the javadoc ;-) |
[12:20]
|
| gambl0re |
then how come its working for me |
[12:20]
|
| gambl0re |
when i do remove method |
[12:20]
|
| gambl0re |
i did set.remove(0) and it worked |
[12:20]
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| Cuckoo` |
It's removing your integer from the set. It is not removing the index of that integer from an array. |
[12:20]
|
| Cuckoo` |
Because it's not an array. |
[12:20]
|
| Cuckoo` |
Behind the scenes there is probably an array with indexes to keep track of what is in that set and where it is in the backing array (an educated guess), but as far as what you're interacting with, there's no method to remove by index as mentioned above |
[12:21]
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[12:21]
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| Cuckoo` |
So, to answer your question, in your case, the thing being removed is literally the integer you passed in. |
[12:22]
|
| gambl0re |
oh so when i was doing set.remove(0) it wasnt removing el from index 0 but rather the literal value of 0 |
[12:22]
|
| gambl0re |
thanks guys |
[12:22]
|
| solvr |
In C/C++ sometimes we on purpose hide the identity of an object, and expose some abstract identifier, like a simple number even, for others to refer to it. Do you do this in Java? |
[12:24]
|
| Kristine86 |
I am trying to parallelize current code that stores values in a single HashMap but in different keys. I'm trying to calculate value for each key in HashMap in a single thread. Currently using newFixedThreadPool. Do I have to use concurrentHashMap, is it recommended? What's your suggestion? |
[12:25]
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| ernimril |
Kristine86, do not modify HashMap from concurrent threads, that never ends well |
[12:26]
|
| ernimril |
Kristine86, so ConcurrentHashMap or some other synchronized version is what you want |
[12:27]
|
| _lucifer |
Cuckoo: its actually backed by a HashMap. |
[12:27]
|
| Cuckoo |
yeah, that's why i said it was a guess, cuz i was totally not sure but in my head an array made some sense |
[12:27]
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| Kristine86 |
ernimril OK I will look into it. So it doesn't limit me from functions I was using for HashMap though right? |
[12:28]
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| _lucifer |
and java's HashMap implementation is very interesting. if the bins exceed a certain size, they are converted to Trees. |
[12:28]
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| ernimril |
Kristine86, Both HM and CHM expose a lot of methods, most of them are the same from a high level perspective |
[12:29]
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| Kristine86 |
OK great! Didn't know about converting it to Trees. Interesting _lucifer |
[12:29]
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| ernimril |
may be converted to trees, if the content is comparable |
[12:30]
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| dmlloyd |
the implementation has changed over time, and will probably continue to change |
[12:30]
|
| ernimril |
and it is something you really do not want to rely on, it means you have a hashCode that is silly, but you have bothered to implement comparable in a sane way |
[12:30]
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| _lucifer |
yeah, it was added as a protection against DDoS attacks iirc. Heinz Kabutz had a nice talk about it. |
[12:32]
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| solvr |
Regarding the lawsuit not that anyone asked, but I wish Oracle won. |
[01:00]
|
| solvr |
But the fact I can steal everyone's API is also cool. |
[01:00]
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| sbalmos |
grr... IDEA's bundled Maven seems to not be parsing ${parent.parent.version} in a plugin version |
[01:02]
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| solvr |
Lenses in Java. Do we need them? |
[01:16]
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[01:16]
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| TheBeastie |
solvr: I do... or I don't see anything :) |
[01:19]
|
| solvr |
Lenses are functions for reading a deeply nested immutable value from an immutable structure, or producing a copy of said deep immutable structure with that deep value changed |
[01:21]
|
| solvr |
Basically it's the immutable version of getter/setter but at arbitrary depth |
[01:21]
|
| solvr |
It's also hurting my brain |
[01:21]
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| dmlloyd |
immutable data structures are very useful in Java but also undersupported |
[01:27]
|
| dmlloyd |
you're not going to have a lot of support for things like lenses, or even e.g. making a new immutable list which consists of the old list plus one item |
[01:27]
|
| dmlloyd |
frameworks like guava give you some of that |
[01:28]
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| solvr |
dmlloyd, they're useful but I wonder if we can't reduce them to mutable collections of immutable records, with implicit relationships, negating the need for immutable structures, lenses etc. |
[01:28]
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| dmlloyd |
in non-concurrent cases, maybe |
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[01:28]
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| dmlloyd |
mutability can become a huge headache in shared structures in multithreaded programs |
[01:28]
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| solvr |
dmlloyd, actually when I think about it, the collections don't have to be mutable. Rather it should be easy to produce "subset" selectors from an immutable large collection. |
[01:30]
|
| solvr |
Hmm |
[01:30]
|
| dmlloyd |
you can, sometimes |
[01:30]
|
| solvr |
Has anyone ever tried mixing immutable structures with elements of relational algebra? |
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| freeone3000 |
solvr: Yes! Lots of people! In the sixties and seventies, in fact. You might be interested in what they came up with. |
[01:36]
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| solvr |
freeone3000, see, no one explicitly mentions relational algebra and functional programming in the same sentence |
[01:36]
|
| freeone3000 |
solvr: Please read *anything* by Edgar F. Codd |
[01:37]
|
| solvr |
freeone3000, I think we've hit the ceiling of snark and sarcasm, and you may need to be a bit more specific |
[01:40]
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| tang^ |
I have a class named EntityObject that extends MutableTreeNode with a method that tries to return children as a Vector<EntityObject>. This is currently running on Java 8. With Java 9+, the return for children changed from Enumeration to Enumeration<? extends TreeNode>. I'm unsure if I can still pack that return into a Vector<EntityObject>. |
[01:40]
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| tang^ |
we have no ceiling for those two things |
[01:40]
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| freeone3000 |
solvr: Start with https://www.seas.upenn.edu/~zives/03f/cis550/codd.pdf |
[01:41]
|
| freeone3000 |
solvr: First paragraph of the paper, after the abstract, directly answers your question. The remainder of the paper addresses solutions. |
[01:41]
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| solvr |
freeone3000 the words functional and immutable are not in this paper |
[01:41]
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| freeone3000 |
solvr: It was the 70s. Immutability was assumed in an n-tuple. Mutability was added later. |
[01:42]
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| freeone3000 |
(Keep in mind we didn't have large amounts of read-write memory yet; this system operated on punched cards.) |
[01:42]
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| solvr |
freeone3000, really. So I guess computers were totally immutable until in the 70s they were like "shit, we can change stuff in memory" |
[01:43]
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| solvr |
So then they needed a word for it |
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[01:45]
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| tang^ |
amazing how that happens, eh? |
[01:46]
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| mbooth |
Wow, I don't know why you bother, freeone3000 |
[01:46]
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| Kristine86 |
can I use threadpool to run just a function rather than creating a new class that implements runnable? |
[01:47]
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| cheeser |
define "threadpool" |
[01:47]
|
| yawkat |
pass a method reference? |
[01:47]
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| Kristine86 |
cheeser I'm just using ExecutorService pool = Executors.newFixedThreadPool(MAX_T); Now I want to use it to call same function but different param for different threads |
[01:49]
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| Kristine86 |
yawkat I'm trying to avoid creating a new class. how do I pass method reference, any example what you mean?> |
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[01:50]
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| yawkat |
this::method |
[01:50]
|
| yawkat |
lambda |
[01:50]
|
| yawkat |
The Java 8 Lambda Expressions Tutorials are located at http://docs.oracle.com/javase/tutorial/java/javaOO/lambdaexpressions.html |
[01:50]
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[01:51]
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| Kristine86 |
so I don't have to implement a new class with Runnable right? Do I still need to create run? Can I avoid that? I'm new to threading. |
[01:52]
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| Maldivia |
method reference |
[01:52]
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| Maldivia |
Maldivia, method reference is a shortcut for a lambda to call a specific method. this::foo for example is equal to () -> this.foo(), and Foo::new equals () -> new Foo(). You can also reference method that require one or more parameters, depending on the functional interface they are to represent. See http://docs.oracle.com/javase/tutorial/java/javaOO/methodreferences.html |
[01:52]
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| cheeser |
you're still creating a new class. you're just leaning on the lambda syntax to do it. |
[01:53]
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[01:54]
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| yawkat |
oh oracle https://s.yawk.at/rH5Se37h |
[01:54]
|
| yawkat |
do you need these to create an account or is there another way? i need to sign the oca |
[01:54]
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| Kristine86 |
cheeser I'm confused. I will work on a code and share. It will probably be helpful to get feedback from that |
[01:56]
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| _lucifer |
yawkat, yeah but i had filled those as N/A when i signed the OCA and it was approved. |
[01:58]
|
| yawkat |
ah, that works. thanks |
[01:58]
|
| cheeser |
yawkat: openjdk stuff? |
[02:02]
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| Maldivia |
Kristine86: at runtime, a lambda or method-reference expression is converted into a class automatically, so you don't see it on disk |
[02:02]
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| yawkat |
cheeser: graal bug |
[02:02]
|
| cheeser |
yawkat: ah. fighting graal (native) myself atm. kotlin coroutines blow up. |
[02:02]
|
| Kristine86 |
Maldivia that makes sense. I'm familiar with lambda exp but not confident how it will act with thread. I'm working on the code to test that. |
[02:03]
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| yawkat |
cheeser: why, do they use reflection? |
[02:03]
|
| yawkat |
i thought they were pretty much compile time |
[02:03]
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| Maldivia |
cheeser: I thought you'd finished that long ago :D |
[02:03]
|
| cheeser |
java.lang.IllegalStateException: @NotNull method kotlin/reflect/jvm/internal/impl/builtins/KotlinBuiltIns.getBuiltInClassByFqName must not return null |
[02:04]
|
| cheeser |
Maldivia: i got it working in jvm mode last week. |
[02:04]
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| yawkat |
well... guess it does :D |
[02:04]
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[02:04]
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| Maldivia |
I seem to trigger Quarkus bugs all the time though, when ever I work on my pet project :D |
[02:04]
|
| yawkat is very proud of making awt work with native-image now |
[02:04]
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| cheeser |
now, it might just be how we're invoking them because we're definitely using reflection (for now) to map the requests coming in. |
[02:05]
|
| cheeser |
i guess i could suck it up and generate the correct code. |
[02:05]
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| yawkat |
i wish graal had a mode where it wrote to stderr when a class.forName fails |
[02:06]
|
| cheeser |
so far i think native mode is overrated. |
[02:06]
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| yawkat |
not hard to add, looking at the graal source, but graal is a pain to build (time and memory wise) |
[02:06]
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| yawkat |
D |
[02:06]
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[02:07]
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| cheeser |
long running processes definitely lag behind the jvm there last time i saw numbers. |
[02:07]
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| yawkat |
yea i get the lambda use case, but beyond that... |
[02:09]
|
| yawkat |
and you dont get shenandoah :( |
[02:09]
|
| yawkat |
i use a java app for my desktop env ( https://github.com/yawkat/wm ) and the fast startup is nice there though |
[02:10]
|
| yawkat |
yawkat's title: "GitHub - yawkat/wm: Panel and tooling for herbstluftwm, written in java" |
[02:10]
|
| yawkat |
and the compiler concept is really interesting... writing the opts in java is much nicer than in c++ |
[02:10]
|
| cheeser |
what does this app do? |
[02:13]
|
| yawkat |
it's just my desktop env, stuff like taskbar and screenshotting and such https://s.yawk.at/7fij8Dta |
[02:14]
|
| yawkat |
from when i had too much time on my hands... |
[02:14]
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| cheeser |
i can see that. :) |
[02:14]
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[02:15]
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| superhanz2 |
hi this is a very basic question. I have a project that relies on a jar file called MASON.20.jar. However, the MASON framework also supports another extension called 2D Physics. The issue I have is how I should use Physics2D. It is not given as a jar file, but rather just as a directory containing its source code |
[02:17]
|
| cheeser |
classpath |
[02:18]
|
| cheeser |
The classpath tells Java or the compiler which jar files and folders to search for classes and resources. Use the -cp/-classpath run-time options to specify the classpath (does NOT work with -jar!). Also see http://bit.ly/15InVZQ [cheeser's blog], http://bit.ly/19MnH5C [oracle.com], or http://bit.ly/2aJ5MoG for more information. |
[02:18]
|
| superhanz2 |
thanks Cheeser |
[02:19]
|
| superhanz2 |
I'll give this a read, see if I can figure it out |
[02:19]
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[02:24]
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| superhanz2 |
hmm okay so having read the first article |
[02:29]
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| superhanz2 |
am I right in thinking that I would add the entire folder of Physics2D to my classpath? (presumably in my .bashrc?) and it doesn't need to be first compiled into a jar file? |
[02:30]
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| dmlloyd |
no, you don't want to do it like that |
[02:30]
|
| superhanz2 |
also I should note I'm using intellij |
[02:31]
|
| dmlloyd |
first you'll need to compile Physics2D |
[02:31]
|
| superhanz2 |
hmm okay so the readme does mention compiling |
[02:31]
|
| superhanz2 |
and I think it has a make file? but I'm not sure how this works, and it isn't really explained |
[02:31]
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| dmlloyd |
most projects use Maven or Gradle to build, but some don't, to their detriment |
[02:32]
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| superhanz2 |
"To install this package, just add the physics2d directory to your CLASSPATH. Alternatively you can unpack the files into the appropriate directories in MASON, or create a jar file and stick that in your CLASSPATH. " |
[02:32]
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| dmlloyd |
I think that might be missing some context |
[02:33]
|
| dmlloyd |
do you have a link? |
[02:33]
|
| superhanz2 |
https://cs.gmu.edu/~eclab/projects/mason/extensions/physics2d/ |
[02:34]
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| dmlloyd |
OK, it's already compiled for you |
[02:35]
|
| superhanz2 |
compiled into a jar file? |
[02:35]
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| cheeser |
compiling and jars are separate concerns |
[02:35]
|
| dmlloyd |
no, but that doesn't matter too much unless you need to repackage it |
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[02:36]
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| superhanz2 |
when you mean its compiled do you mean the .java files are compiled into .class files? |
[02:36]
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| dmlloyd |
so now if you want to use both this and the MASON.20 thing, you'd use a class path that looks like `/path/to/physics2d:/path/to/MASON.20.jar` |
[02:36]
|
| dmlloyd |
yes |
[02:36]
|
| superhanz2 |
ah great, I'll give that a try. |
[02:37]
|
| dmlloyd |
if your project has no build system configuration, then the way to do this is to go into "project structure", add both of those items (one directory and one JAR file) as "Libraries", and then add those two libraries to your module's "Dependencies" |
[02:37]
|
| dmlloyd |
(this is in IntelliJ, since you said that's what you're using) |
[02:38]
|
| dmlloyd |
then you're good to go for development |
[02:38]
|
| dmlloyd |
IntelliJ should allow you to create run configurations from this setup |
[02:38]
|
| superhanz2 |
I've already added the mason jar file. If I were to add the Physics2D directory, doing this is adding it to the classpath? |
[02:39]
|
| superhanz2 |
I wouldn't have to add anything to my .bashrc, say? |
[02:40]
|
| dmlloyd |
yes. be aware that "classpath" is an abstract term |
[02:40]
|
| dmlloyd |
in general you don't want to do anything related to classpath in your shell |
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| superhanz2 |
brilliant it seems to have worked |
[02:43]
|
| superhanz2 |
thanks so much dmlloyd |
[02:44]
|
| dmlloyd |
? |
[02:44]
|
| superhanz2 |
i think you've cleared up what I've actually done to get it working, so I'm no longer just blindly trying new things until it works with no idea why |
[02:44]
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[02:49]
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| twodee23 |
Hi, I'm trying to understand Event Sourcing and CQRS and applying it with Java. I understand that there has to be an event bus that will trigger services based on events. On the read side, I'll have a read model derived from those events and there will be a separate db on the write side. What is typically stored on the write side? The event store? Or something like an updated consistent state? |
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[03:29]
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| solvr |
Does it make sense to have a trie represent a list of records, and when I build an index on those records... that's also a trie with the same topology. So when I select a subset of records, I select the same segments from the index trie, and I'll have less false positives when reusing the index? |
[03:30]
|
| cheeser |
you want a database |
[03:32]
|
| solvr |
cheeser, databases don't even do this |
[03:33]
|
| cheeser |
you're so cutting edge, eh? |
[03:33]
|
| solvr |
cheeser, also not sure how many times I said the data comes from a database |
[03:33]
|
| Diablo-D3 |
so why not just query that db?! |
[03:33]
|
| solvr |
Because that's not the point at all |
[03:33]
|
| Diablo-D3 |
then whats the point?! |
[03:33]
|
| Diablo-D3 |
what are you *actually* trying to solve?! |
[03:34]
|
| _lucifer |
so you think you can beat the performance of the db? |
[03:34]
|
| solvr |
Well apparently it's hard to explain |
[03:34]
|
| ernimril |
solvr, consider giving concrete example of what you are trying to do if you want help. |
[03:34]
|
| Diablo-D3 |
its like you're badly reimplementing a db cache |
[03:34]
|
| solvr |
_lucifer, not the point at all either |
[03:34]
|
| solvr |
Well what I was asking is index trie. |
[03:34]
|
| solvr |
Does that make sense |
[03:34]
|
| cheeser |
no. use a database. |
[03:34]
|
| solvr |
So index trie it is |
[03:35]
|
| ernimril |
solvr, I think you want to have an unlimited number of attributes and have index lookups for all attributes and that wont work well |
[03:35]
|
| solvr |
Not all attributes at all. |
[03:36]
|
| solvr |
Just ones acting as PK or FK |
[03:36]
|
| ricky_clarkson |
ernimril: Isn't that what columnar DBs achieve? |
[03:36]
|
| cheeser |
so ... attributes, then. |
[03:36]
|
| solvr |
My problem is that when I select a subset of a collection of records, my indexes are useless |
[03:37]
|
| solvr |
I wanna ship usable indexes with that subset |
[03:37]
|
| cheeser |
apply more than one index? |
[03:37]
|
| ernimril |
ricky_clarkson, try having 50 attributes and setup index on all of them and try grabbing searches by random attributes, first one and then some of the others and see if you can guarantee any good performance |
[03:37]
|
| solvr |
So efficiently reducing false positives is essential |
[03:37]
|
| solvr |
Some false positives is OK |
[03:37]
|
| ricky_clarkson |
ernimril: BigQuery basically does that, without any manual indexing setup. |
[03:37]
|
| solvr |
(false positive = the index points to a record that's not in the subset) |
[03:38]
|
| ernimril |
solvr, as I said before there are multi-dimensional indexes for example my prtree, but I guess you did not look at that |
[03:38]
|
| ricky_clarkson |
based on the original Dremel whitepaper that led to some open source impls |
[03:38]
|
| solvr |
ernimril, prtree is interesting but not what I want, because the subset is not known in advance |
[03:38]
|
| ernimril |
ricky_clarkson, the problem is that you will get some combinations that are horrible for performance |
[03:38]
|
| ricky_clarkson |
In the BQ case that will happen with data skew, just 1 machine will process 90% of the data. |
[03:39]
|
| ricky_clarkson |
that's for joins but for straight queries there's no such problem |
[03:39]
|
| solvr |
Also maybe I don't need a trie, per se, I just need segments, flat segments even |
[03:39]
|
| ernimril |
solvr, well until you can explain your question you will probably not get help |
[03:39]
|
| solvr |
ernimril, I did explain it. You have a list of records, and in index on them. Some random criteria selects a subset of them. I want the indexes I have to be usable with that subset |
[03:40]
|
| solvr |
ernimril, to be usable we need to reduce false positives to something less than 50% |
[03:40]
|
| ernimril |
solvr, consider asking question with enough contexts that other people can understand, preferably with a few examples |
[03:40]
|
| solvr |
The less the better |
[03:40]
|
| ernimril |
solvr, so setup an index for each and do a hash-join on the index lookups? |
[03:41]
|
| solvr |
index for each what |
[03:41]
|
| ernimril |
solvr, you previously mentioned something like 1000 records so you can do whatever you want with that in memory without it taking any time |
[03:42]
|
| ernimril |
solvr, each attribute you want to search for |
[03:42]
|
| Diablo-D3 |
so whats wrong with throwing h2 at it? |
[03:42]
|
| Diablo-D3 |
export from db, import into your db, go ham |
[03:42]
|
| solvr |
ernimril, I mentioned 1000 but what I didn't mention is the n^m complexity of looking those up recursively to build, say, a graph they represent |
[03:42]
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[03:43]
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| ernimril |
solvr, what did I say about asking question with enough contexts? |
[03:43]
|
| solvr |
Well there it is |
[03:43]
|
| solvr |
) |
[03:43]
|
| ernimril |
solvr, no, there it is not |
[03:44]
|
| solvr |
I feel like the only way to provide enough context is to pull down my pants and reveal my most sacred secrets |
[03:44]
|
| solvr |
Anyway. |
[03:44]
|
| solvr |
I tried to explain as well as I could. |
[03:44]
|
| _lucifer |
do you see measurable performance degradation when using the tools available or is it this all out of thin air? |
[03:44]
|
| solvr |
Thanks for the feedback |
[03:44]
|
| ernimril |
solvr, we do not care about your private parts, keep them to yourself |
[03:45]
|
| solvr |
ernimril noted |
[03:45]
|
| ernimril |
solvr, if you want help you have to explain enough for us to actually understand |
[03:45]
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[03:45]
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| solvr |
ernimril, I'll give it a last shot. And present the situation in two parts. |
[03:46]
|
| solvr |
Part 1) you have a graph as a flat list of users forming a graph. Between 200 and 10k items typically. You want to build that graph as an object graph in memory. How would you |
[03:47]
|
| ernimril |
solvr, also: consider that a data structure discussion is not something secret, having a program that works well enough and a userbase is what you want |
[03:47]
|
| solvr |
ernimril, I have no secrets, I'm just trying to explain the class of problems I'm looking at |
[03:48]
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| solvr |
Sorry for the nonsense |
[03:48]
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| ernimril |
solvr, I decide the data structure and the algorithms to use first when I know what question I need to answer |
[03:48]
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| solvr |
I'd solve part 1 by building a Map<> index on the attributes I want to connect, and then recursively matching the index to the attributes building a graph |
[03:49]
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| solvr |
So far so good, that works fine. And mostly O(N) speed |
[03:49]
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| ernimril |
solvr, so for now a Set of objects, and some way to say "what are the neighbours of this thingy". For example a Map<ItemId, Item> where each item has a List<ItemIds> neighbours |
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[03:50]
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| solvr |
Right |
[03:50]
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| solvr |
So here comes part 2 |
[03:50]
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| deepy |
With javafx after 8 I don't seem to be able to add things to the pre-existing context-menu, only to set a new context-menu, is there some helper for re-adding the Select All/Copy/Paste/etc? |
[03:51]
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| solvr |
Part 2) from this initial list of users, which list now has the necessary indexes in Maps to build graph from, I have an arbitrary filter() lambda, that picks SOME subset of those users. I need to pass this subset of users to another method, but I want to pass it with a usable subset of the indexes I have so they don't have to rebuild them from |
[03:51]
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| solvr |
scratch. |
[03:51]
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| solvr |
So they can also build a graph. From the subset I gave them |
[03:52]
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| solvr |
If I pass the full indexes, looking up will produce tons of false positives where the index points to users which are NOT in the subset |
[03:53]
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| solvr |
Having some false positives is OK, if it doesn't make the index pointless. |
[03:53]
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| ernimril |
solvr, again, too little information. Arbitrary filter does not make sense. |
[03:54]
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| solvr |
It's arbitrary. |
[03:54]
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| solvr |
Some lambda I'm given from elsewhere. |
[03:54]
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| ernimril |
solvr, so it can be a filter on _every_ attribute you have? |
[03:54]
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| solvr |
It's opaque to me. A subset is selected, I know what that subset is. I don't know it in advance tho |
[03:54]
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| ernimril |
solvr, the filter can depend on the phase of the moon? |
[03:54]
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| solvr |
ernimril, it can even be a filter on info outside the records for all I know. Might include current time or phase of moon. Arbitrary lambda |
[03:55]
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| ernimril |
solvr, then you can not setup any index that will work so why even try? |
[03:55]
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| solvr |
ernimril, the index is on my PK/FK attributes. The filter doesn't use those indexes. But after I pass the subset to method FOO() , that method will NEED indexes on PK/FK on that subset I gave it |
[03:56]
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| solvr |
Story so far: (list of users + indexes on PK+FK) -> (comes along wild filter(lamdba), picks a subset) -> (method FOO() receives the subset, and needs to look things up by PK/FK) |
[03:57]
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| ernimril |
solvr, what is your pk/fk? an int? an uuid? a string? Do you not have a Map<Id, Item> that you can use to find items by pk/fk? |
[03:58]
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| solvr |
ernimril, it varies, but yes, a Map is OK |
[03:59]
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| ernimril |
solvr, so Foo() can grab an item by the key in O(1) time, so what is the problem? |
[03:59]
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| solvr |
ernimril, the problem is this map covers the full list, not the sublist |
[03:59]
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[03:59]
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| ernimril |
solvr, so? why does that matter? you are looking up things by id |
[04:00]
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| ernimril |
solvr, passing the Map is just passing one reference so that is cheap |
[04:00]
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| solvr |
ernimril, so imagine FOO() looking things up by PK in an 1:N relationship. It finds a list of N items. Loops through them, most are not even in the subset |
[04:00]
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| ernimril |
solvr, so, a check that the found item is in the sublist is another map lookup, another O(1) operation (as long as you prepare the input into a map or a set) |
[04:02]
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| ernimril |
solvr, so you have two O(1) operations, is that heavy calculations? |
[04:02]
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| solvr |
ernimril it becomes O(N) over a list of N items, and if you do this recursively to build a graph, it become N^M |
[04:03]
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| solvr |
Where M is the depth of the graph |
[04:03]
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| ernimril |
solvr, so here is another thing about missing context |
[04:04]
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| _lucifer |
i just noticed "Remove the Experimental AOT and JIT Compiler" is JEP 410. (410 Gone) ? |
[04:04]
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| yawkat |
D |
[04:05]
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| ernimril |
solvr, and I think you overestimate things. How many recursions do you do? |
[04:05]
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| solvr |
ernimril, unknown but probably max sqrt(list size) |
[04:06]
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| ernimril |
solvr, is that <10 <1000 <1000000 ? |
[04:06]
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| solvr |
< 1000 |
[04:07]
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| ernimril |
solvr, so that rules out ordinary recursion, you will hit stack overflow. Sorry, but you have to rewrite to some other type of loop |
[04:07]
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| ricky_clarkson |
Trampoline! |
[04:07]
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| solvr |
Wait, the stack is that small? |
[04:07]
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| solvr |
Well anyway I can write it as a loop with a manual stack |
[04:08]
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| solvr |
Complexity remains the same tho |
[04:08]
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| ernimril |
solvr, so how large is N? |
[04:09]
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| ernimril |
solvr, and how long time do you have to run every query? |
[04:09]
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| solvr |
ernimril, see, this is why I don't wanna explain much. |
[04:09]
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| solvr |
ernimril, I appreciate one needs context |
[04:10]
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| solvr |
But there's just too much context |
[04:10]
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| solvr |
Thanks ernimril, I'll think about it more |
[04:10]
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| ernimril |
solvr, ok, go and figure this out on your own, not sure why you ask questions if you do not want to discuss the issue? |
[04:10]
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| solvr |
Well, I don't wanna fill the entire thread with minutae of my BS |
[04:11]
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| ricky_clarkson |
I respect Scheme implementations, rather than stack overflow they put the stack on the heap just before overflow and point back at the beginning of the stack. |
[04:11]
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| solvr |
I thought maybe I'm missing something obvious |
[04:11]
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| yawkat |
much too late for that lol |
[04:11]
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| solvr |
And I did get interesting pointers from you and others |
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| solvr |
yawkat, we're event-sourced here, I can only apply a transaction reversing "mea culpa" event. |
[04:12]
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| _lucifer |
if and when you solve your problem, i would be interested in knowing how much performance you gained by not using an existing solution. |
[04:13]
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| solvr |
_lucifer, prolly something trivial. |
[04:14]
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| solvr |
I do it for (shitty) science I guess |
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| _lucifer |
this is isn't science but nvm. |
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[04:16]
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| solvr |
_lucifer it is when I'm stupid |
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[05:04]
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| Kristine86 |
How do I make this work without using implements Runnable? https://pastebin.com/Hru1XL3U |
[05:10]
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| cheeser |
execute( () -> { sleep(1000); println(); map.put("fast", "fast"); } ); |
[05:14]
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| Kristine86 |
That is just a sample code in fn method though. I need to put a large block of code there. |
[05:15]
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[05:15]
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| cheeser |
ok. put that large block in a method and call it from there. |
[05:16]
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| cheeser |
execute( () -> { largeBlockOfCode(); } ); |
[05:16]
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| cheeser |
magic! |
[05:16]
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| Kristine86 |
haha yes it works now thanks. |
[05:18]
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| Kristine86 |
I was forgot before ()-> and I thought execute needed Runnable object in there. |
[05:18]
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| Kristine86 |
testing it now |
[05:18]
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| cheeser |
it does. but you can hide that with the right syntax. |
[05:18]
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| cheeser |
are you using IDEA? |
[05:19]
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| Kristine86 |
me? What do you mean, what IDEA? |
[05:19]
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| cheeser |
what IDE are you using? |
[05:19]
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| Kristine86 |
eclipse, but I need to run in a remote machine. Why? |
[05:20]
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| cheeser |
well, i had an IDEA tip but it's not applicable if you're using eclipse |
[05:22]
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| Kristine86 |
pool.awaitTermination(Long.MAX_VALUE, TimeUnit.NANOSECONDS); is this a right efficient statement to wait for threads to end? |
[05:24]
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| mbooth |
An efficient way to wait...? |
[05:25]
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| Kristine86 |
Yes. Or could it cause longer delay than needed? |
[05:25]
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| ricky_clarkson |
an efficient way of waiting for potentially 292 years. Interesting ;) |
[05:26]
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| Kristine86 |
well if threads end sooner it would too thought right? |
[05:26]
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| ricky_clarkson |
sir, you waited for 292 years and 2 seconds, that's a hard fail |
[05:27]
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| Kristine86 |
ricky_clarkson I know what you did there :P |
[05:27]
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| cheeser |
to be fair, the waiting is the hardest part. |
[05:29]
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| freeone3000 |
use an actual reasonable value there, please. |
[05:30]
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| freeone3000 |
this is like, advanced programming 201: nothing is actually infinite. instead, set it to be finite, but larger than you'll ever need -- so if it turns out you were wrong, on either end, you can figure out why. |
[05:31]
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| freeone3000 |
if your threads aren't terminating, that's a problem! that problem needs to be solved! If killing the threads when they don't terminate cause a problem, well, that'd also cause a problem if they were killed for any other reason, so that needs to be solved to. reliability and consistency. |
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| Kristine86 |
ah ok got it. |
[05:37]
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| Kristine86 |
I just need to parallelize the actual code |
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| jrandom |
If I have a type T for a class example, `public class Foo<T> {}` how can I restrict this type `T` such that type which implements `compareTo()` method (I think there is an interface for that in Java right?) will only be allowed. And type which do not implement that method isn't allowed. How can I do that? |
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[08:27]
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| jrandom |
What I need to do to `Foo` such that only types `T` which implements `Comparable`(which impelments the method .compareTo() since we make use of that inside) is only allowed? |
[08:28]
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| jrandom |
Ok, looks like I need to do something like `public class Foo<T extends Comparable>{}` |
[08:32]
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| dreamreal |
Comparable<T> probably |
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[08:52]
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| freakz |
Hi everyone, I finally complete the official tutorial |
[08:52]
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| freakz |
I'm looking for a good book to go deeper |
[08:53]
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| freakz |
the most recommanded is Head First Java |
[08:53]
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| freakz |
it seems too old no ? |
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| jrandom |
If i have a member variable which if type `List<T> list;` where T is a generic type(like before which extends Comparable), How can I instanciate the type `List<T> list;` in the constructor of class `Foo`? |
[09:04]
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| jrandom |
nevermind, List is an interface. |
[09:17]
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| jrandom |
my bad |
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