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FAQ Explanations

 
Greenhorn
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Hi All,

May I ask to explain me following point from FAQ:

Local classes cannot access non-final variables.



Thank you.

 
Ranch Hand
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There's a good detailed explanation for this in the K&B SCJP6 book on page 671, in the section Method-Local Inner Classes

From reading the above section:

Method-Local inner classes are declared inside a method.

Variables declared inside a method reside on the stack ( not on the heap) and so, they are temporary.

But the object created from the Method-Local inner class can exist on the heap long after the method completes, so it needs to guarantee that whatever variables it is accessing still exist on the heap ( I think final variables declared inside a method exist permanently and that's why it can access only final variables and not regular variables declared inside the method.)

If the variable accessed inside the method-local inner class is a variable from the outer class (not a method variable) , it need not be declared final. The outer object's variables exist on the heap.

Only if the variable accessed in the method-local inner class is a variable declared inside the method, then that variable can be accessed only if it is final , otherwise the code throws a compiler error.




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