I once in the not-too-distant past had a Developer interview go comically off the rails when I (the interviewee) was posed with the simple software development question:
"Describe the difference between a value type variable and a reference type variable"
This is an elementary Comp Sci 101 question that every developer should be able to understand and answer with unflinching confidence.
This is what value type (int a left) and reference type (object a on the right) memory allocation looks like graphically
The correct answer would point out that value type variables ('primitive' in Java) are stored directly in memory within the Stack while reference type variables contain pointers (id) to another memory location in the Heap (which may in turn contain additional memory references (pointers) that compose the entire object).
And (no I swear really) at one point I knew exactly what the difference was. However with time and as development languages and tools become more and more abstracted away from the underlying behavior of memory during application run-time, my knowledge of this simple-yet-important concept went blank.
I stammered though a meandering non-answer about how value types contain "simple" data types that are known as primitives and how reference types refer to more complex objects. Suffice it to say that it was an embarrassing lack of clarity and awareness of how application memory works and likely torpedoed any chance of an offer.
On value and reference types, the Stack and the Heap and Boxing/Unboxing (converting between val and ref)
This is something we should all know as developers. I hope this helped refresh and/or clarify the concept of variable memory allocation for at least a few people out there.
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