Why Java inner classes require "final" outer instance variables? -

-

this question has answer here:

final jtextfield jtfcontent = new jtextfield(); btnok.addactionlistener(new java.awt.event.actionlistener(){     public void actionperformed(java.awt.event.actionevent event){         jtfcontent.settext("i ok");     } } );

if omit final, see error "cannot refer non-final variable jtfcontent inside inner class defined in different method".

why must anonymous inner class require outer classes instance variable final in order access it?

well first, let's relax, , please put gun down.

ok. reason language insists on cheats in order provide inner class functions access local variables crave. runtime makes copy of local execution context (and etc. appropriate), , insists make final can keep things honest.

if didn't that, code changed value of local variable after object constructed before inner class function runs might confusing , weird.

this essence of lot of brouhaha around java , "closures".

note: opening paragraph joke in reference all-caps text in original composition of op.


Comments

Post a Comment

Popular posts from this blog

java - Oracle EBS .ClassNotFoundException: oracle.apps.fnd.formsClient.FormsLauncher.class ERROR -

-
i need in configuring java on machine because, when try loading forms, loader goes in circles , gives error: java.lang.classnotfoundexception: oracle.apps.fnd.formsclient.formslauncher.class @ sun.plugin2.applet.applet2classloader.findclass(unknown source) @ sun.plugin2.applet.plugin2classloader.loadclass0(unknown source) @ sun.plugin2.applet.plugin2classloader.loadclass(unknown source) @ sun.plugin2.applet.plugin2classloader.loadclass(unknown source) @ java.lang.classloader.loadclass(unknown source) @ sun.plugin2.applet.plugin2classloader.loadcode(unknown source) @ sun.plugin2.applet.plugin2manager.createapplet(unknown source) @ sun.plugin2.applet.plugin2manager$appletexecutionrunnable.run (unknown source) @ java.lang.thread.run(unknown source) i have tried re-installing firefox, older versions of java runtime environments, disabling proxy. what missing? application working on other machines. i spent around 100 hours finding s...
Read more

c# - how to use buttonedit in devexpress gridcontrol -

-
Image
i trying create gridcontrol buttonedit in 1 of columns. when user clicks button edit, popups form select product. when selection done on popup, returns datarow selection main grid below. but when column loses focus, value wrote column disappear. here code creates gridcontrol's data , buttonedit's click event. private void frmsiparisnew_load(object sender, eventargs e) { dt = new datatable(); dt.columns.add("malzeme_kodu",typeof(string)); dt.columns.add("malzeme_aciklama", typeof(string)); dt.columns.add("adet", typeof(decimal)); dt.columns.add("birim", typeof(string)); dt.columns.add("fiyat", typeof(decimal)); dt.columns.add("kur", typeof(string)); dt.columns.add("tutar", typeof(decimal)); datarow dr = dt.newrow(); dt.rows.add(dr); gc.datasource = dt; } private void repositoryitembuttoneditmal...
Read more

How do you convert a timestamp into a datetime in python with the correct timezone? -

-
you naively expect work: import pytz datetime import datetime def tz_datetime_from_timestamp(timestamp): """convert timestamp datetime """ tz = pytz.timezone('australia/perth') server_time = datetime.utcnow() delta = tz.utcoffset(server_time) value = datetime.utcfromtimestamp(timestamp).replace(tzinfo=tz) return value + delta print tz_datetime_from_timestamp(1416387060) and convert timestamp 1416387060 wed nov 19 16:51:00 2014 gmt+8:00. ...but not. prints: 2014-11-19 16:51:00+07:43 the timezone of australia/perth not gmt+7:43. it gmt+8:00. unequivocally stated on australian government website http://www.australia.gov.au/about-australia/our-country/time : awst equal coordinated universal time plus 8 hours (utc +8). so, heck pytz pulling 7.43 from? well, turns out pytz pulls data http://www.iana.org/time-zones time zone database, , database states: # western australia # # rule name type in on @...
Read more