12: Passing and returning objects

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By
this time you should be reasonably comfortable with the idea that when
you’re “passing” an object, you’re actually passing a
handle.

In
many programming languages, if not all of them, you can use that
language’s “regular” way to pass objects around and most of
the time everything works fine. But it always seems that there comes a point at
which you must do something irregular and suddenly things get a bit more
complicated (or in the case of C++, quite complicated). Java is no exception,
and it’s important that you understand exactly what’s happening
with them as you pass them around and assign to them. This chapter will provide
that insight.

Another
way to pose the question of this chapter, if you’re coming from a
programming language so equipped, is “Does Java
have pointers?” Some have claimed that pointers are hard and dangerous
and therefore bad, and since Java is all goodness and light and will lift your
earthly programming burdens, it cannot possibly contain such things. However,
it’s more accurate to say that Java has pointers; indeed, every object
identifier in Java (except for primitives) is one of these pointers, but their
use is restricted and guarded not only by the compiler but by the run-time
system. Or to put in another way, Java has pointers, but no pointer arithmetic.
These are what I’ve been calling “handles,” and you can think
of them as “safety pointers,” not unlike the safety scissors of
elementary school- they aren’t sharp so you cannot hurt yourself without
great effort, but they can sometimes be slow and tedious.

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