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The user refractedthought at reddit had the best explanation IMO: Ok, I think the real losers in this discussion are the ones who fail to see both sides of the

The user refractedthought at reddit had the best explanation IMO: Ok, I think the real losers in this discussion are the ones who fail to see both sides of the issue. We can cherry pick "refrence" definitions if we want, but really the nuts and bolts come down to this: Passing by value means that a copy of the parameter is made when the function is called and any changes to that variable will not be reflected outside of the function. Passing by reference means you pass a pointer to your data (and nothing more) so the function can dereference the parameter and affect data that exists outside of the function. All non-primitives in Java are implicit pointers, so when you pass one of these into a function, you are passing a pointer (or reference) to data that exists outside of the function. However, the reference itself, as it exists inside the function, can be changed to point toward something else. Essentially, the implicit pointer is passed by value, and that value can be altered without affecting anything outside the function. So technically yes, you could get away with calling this pass-by-value. However, the spirit of pass-by-reference is maintained for any part of the data that most people care about. The syntax is different from a pass-by-reference in C++, and there's a silly little trick you can do by changing the reference pointer (or silly trick you can't do by changing the pointer outside the function) but for all practical purposes you are doing the same thing. In my opinion, if you want to insist that Java strictly follows pass-by-value, then I think it has ceased to be a relevant distinction.

scott_s 17y ago
dschobel's comment clearly demonstrates how the distinction between pass-by-value and pass-by-reference in Java is not purely academic: http://news.ycombinator.com/item?id=979799 http://news.ycombinator.com/item?id=979799 It's a relevant distinction because it's required to explain code behavior.
rbanffy 17y ago
"it has ceased to be a relevant distinction." I think this distinction ceased to be relevant in the late 70's...
dkarl 17y ago
So technically yes, you could get away with calling this pass-by-value. However, the spirit of pass-by-reference is maintained for any part of the data that most people care about. And if there's any time you can afford to be loose about the spirit vs. the "technical" letter of the thing, it's when you're talking to a compiler. Right? I agree with the article. If you don't like the meaning of a technical term with a clear meaning, or if you simply don't have any occasion to use it properly, that's no excuse for repurposing it in the same context to mean something different that leads to confusion. It's worthwhile to remember that (true) pass by reference isn't just a curiosity from obsolete languages. It's common for people entirely new to programming to expect that function parameters might, or actually do, work that way. The terms are at least useful to explain things to new learners. In my opinion, if you want to insist that Java strictly follows pass-by-value, then I think it has ceased to be a relevant distinction. Even if you work only with pass by value languages, you should still respect the terminology. Some mathematicians only work with continuous functions, but they don't say, "Hey, this word 'continuous' would be a lot more useful if we redefined it to draw a useful distinction among the functions we actually work with." So "pass by reference" doesn't mean what you want it to mean and doesn't seem very useful to you. Invent your own terminology. Don't destroy existing terminology by sowing confusion. And that's all you can accomplish -- there are too many people walking around who already know what "pass by reference" means for you to get away with redefining it.
mpakes 17y ago
I strongly disagree. Proper terminology is incredibly relevant. As stated in the original article, pass-by-value and pass-by-reference have well-known definitions within the computer science community. There is no ambiguity here. When we excuse the lazy use of such terms incorrectly, we hamper the ability to communicate clearly and effectively. Please stop. The core misunderstanding seems to be a conflation of 'pass a reference by value' and 'pass-by-reference'. Passing a reference by value != pass-by-reference. The End. Q.E.D. Pass-by-reference means that the compiler takes a reference of (or, getting a pointer to) the parameter passed in to the function. This is not the same as passing an existing reference (pointer) to the function (by value). Java only allows the latter (primitive types aside). A side issue is that some developers mistakenly believe that pass-by-value roughly implies a deep copy, and thus that the 'spirit' of pass-by-reference is the avoidance of a deep copy. I would posit that many C++ functions that operate on object parameters do so via a pointer (a.k.a. reference) passed by value, just as Java does: void modify_my_object(MyClass *myObject) { myObject.setName("New Name"); } int main(void) { MyClass *myObject = new MyObject("A Name"); modify_my_object(myObject); // myObject.name is now "New Name" } This is pass-by-value, and there is no deep-copy happening there. Just because many developers don't take advantage of (or don't understand the semantics of) pass-by-reference does not excuse ignorance of the well-known definitions of those terms.

scott_s 17y ago

dschobel's comment clearly demonstrates how the distinction between pass-by-value and pass-by-reference in Java is not purely academic: http://news.ycombinator.com/item?id=979799 http://news.ycombinator.com/item?id=979799 It's a relevant distinction because it's required to explain code behavior.

rbanffy 17y ago

"it has ceased to be a relevant distinction." I think this distinction ceased to be relevant in the late 70's...

dkarl 17y ago

So technically yes, you could get away with calling this pass-by-value. However, the spirit of pass-by-reference is maintained for any part of the data that most people care about. And if there's any time you can afford to be loose about the spirit vs. the "technical" letter of the thing, it's when you're talking to a compiler. Right? I agree with the article. If you don't like the meaning of a technical term with a clear meaning, or if you simply don't have any occasion to use it properly, that's no excuse for repurposing it in the same context to mean something different that leads to confusion. It's worthwhile to remember that (true) pass by reference isn't just a curiosity from obsolete languages. It's common for people entirely new to programming to expect that function parameters might, or actually do, work that way. The terms are at least useful to explain things to new learners. In my opinion, if you want to insist that Java strictly follows pass-by-value, then I think it has ceased to be a relevant distinction. Even if you work only with pass by value languages, you should still respect the terminology. Some mathematicians only work with continuous functions, but they don't say, "Hey, this word 'continuous' would be a lot more useful if we redefined it to draw a useful distinction among the functions we actually work with." So "pass by reference" doesn't mean what you want it to mean and doesn't seem very useful to you. Invent your own terminology. Don't destroy existing terminology by sowing confusion. And that's all you can accomplish -- there are too many people walking around who already know what "pass by reference" means for you to get away with redefining it.

mpakes 17y ago

I strongly disagree. Proper terminology is incredibly relevant. As stated in the original article, pass-by-value and pass-by-reference have well-known definitions within the computer science community. There is no ambiguity here. When we excuse the lazy use of such terms incorrectly, we hamper the ability to communicate clearly and effectively. Please stop. The core misunderstanding seems to be a conflation of 'pass a reference by value' and 'pass-by-reference'. Passing a reference by value != pass-by-reference. The End. Q.E.D. Pass-by-reference means that the compiler takes a reference of (or, getting a pointer to) the parameter passed in to the function. This is not the same as passing an existing reference (pointer) to the function (by value). Java only allows the latter (primitive types aside). A side issue is that some developers mistakenly believe that pass-by-value roughly implies a deep copy, and thus that the 'spirit' of pass-by-reference is the avoidance of a deep copy. I would posit that many C++ functions that operate on object parameters do so via a pointer (a.k.a. reference) passed by value, just as Java does: void modify_my_object(MyClass *myObject) { myObject.setName("New Name"); } int main(void) { MyClass *myObject = new MyObject("A Name"); modify_my_object(myObject); // myObject.name is now "New Name" } This is pass-by-value, and there is no deep-copy happening there. Just because many developers don't take advantage of (or don't understand the semantics of) pass-by-reference does not excuse ignorance of the well-known definitions of those terms.