Casting generics list in Java -


i found weird situation when casting generics. run code:

class { }  class b { }  public class program {      @suppresswarnings("unchecked")     public static void main(string[] args) {         list<a> lista = new arraylist<a>();         list<?> list = lista;         ((list<b>)list).add(new b());          (object item : lista) {             system.out.println(item.tostring());         }     } }

it compiles (only warning without error) , run without exception , output was:

b@88140ed

how did that? mean why java allow me such thing? added instance of b class list of as?

it bad behaviour of generics. why happening?

btw, tried java 7.

edit:
surprised me java notify problem warning every programmer can ignore it. know suppresswarnings bad idea, why java didn't denied such behavior error or exception?

in addition, warning showed always, if think casting correct have no choice ignore it. if think casting , ignore isn't?

every programming language allows shoot foot.

in case, java in dilemma: keep generics information in bytecode , break millions of lines of existing code or silently drop generics information after compiler has it's utmost check , keep backward compatibility.

the java team decided latter , introduced type erasure - which has flaws. if had broken millions of fine (if type-wise incomplete) lines of java code, people have shown pitchforks , burning torches ...


Comments

Post a Comment

Popular posts from this blog

angularjs - ADAL JS Angular- WebAPI add a new role claim to the token -

i have created angular spa webapi backend using adal js authentication.as there no roles in ad, need manually add role claims in order give users access different api controllers. the roles stored in database. expecting inject claim through call webapi after authentication ad. webapi code might this. identity.addclaim(new claim("role", "user")); var ticket = new authenticationticket(identity, props); var accesstoken = startup.oauthbeareroptions.accesstokenformat.protect(ticket); is possible replace adal idtoken new token? is viable solution or there other better way handle this? as initial token generated azuread, possible edit token add new claim? appreciated. graph api supporting group claims. see here: http://justazure.com/azure-active-directory-part-4-group-claims/ if @ examples on page, users assigned groups , app can check group in claims. in current version of portal, need app manifest , modify it.
Read more

php - CakePHP HttpSockets send array of paramms -

i problem when make request (i can request). $link = 'http://uri/path/?param1=1&sid=2&sid=3&sid=4' $http = $httpsocket = new httpsocket(); $res = $httpsocket->get($link); if check request pr($http); i see : [line] => /url/path/?param1=1&sid%5b0%5d=2&sid%5b1%5d=3&sid%5b2%5d=4 http/1.1 and i'm getting empty response because server doesn't know parameters sid%5b0%5d=2 when try send parameters array : $data = array('param1' => '1', 'sid' => array('2','3', '4')); i see same changes %5b0%5d - additional indexes. how fix it? unfortunately , can not change server side, if send request in browser, i'll normal response in json format. when make request, can parameters this: $param1 = $_get['param1']; $sid= $_get['sid']; tip: use diferente names parameters. have multiples sid. use sid1, sid2, sid3... update: can parameters this:
Read more

node.js - Using Node without global install -

i'm working on few node & electron (atom shell) projects , i'm curious how them work without user having install node globally. i've seen few applications including node directory in project contains node.exe binary. how go setting node project use binary? edit: thought should add, i've searched everywhere answer this, unrelated results.
Read more