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

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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.


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