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'final' local variables

 
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I'm studying the SCJP 1.5 book by Kathy Sierra and Bert Bates, and have the following question (related to pages 645 and 646):

Why can 'final' local variables be referenced in a method-local inner class? That is, what impact does the 'final' modifier have on the variable's lifecycle/scope or garbage collection?

Example (from book) where variable z must be 'final':

 
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Welcome to JavaRanch!

Let us know if this thread answers the question.
 
Cindy Rogers
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Yes, thanks!

Cindy Rogers
 
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method vars exist on stack, instance vars exist on heap. Since method local class instances or anonymous instances may be passed out of the method as part of a return value, they are required to exist after the lifetime of the method. The compiler accomplishes this by copy them from stack to heap. How you have a copy of the var on the heap this extends lifetime of the variable beyond the method scope. This stack->heap copy process is only done for final variables so they can exist outside of their method scope.
 
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