5 ms·

Well, that's just the little difference I mentioned about C conflating arrays and pointers to them. The char ^ is being viewed as an array, which in C happens t

by kbp 8y ago

Well, that's just the little difference I mentioned about C conflating arrays and pointers to them. The char ^ is being viewed as an array, which in C happens to be synonymous with a pointer to the start of the array. It's certainly not inherent to pointers that they be mixed up with arrays like that (or to strings that they be represented as char arrays). As an aside, C's conflation of arrays and pointers was done because they're very closely related, and you can get very similar results to a C pointer-to-pointer by wrapping an object in a one-element array. In C, ^x is equivalent to x[0], and Java doesn't have ^x, so you can just use x[0]. More generally, though, a C programmer is virtually never thinking of 'the address 54fc892d': unless they're doing really low-level stuff, they won't think of it like that any more than a Java programmer, even using pointers all day, just like the Java programmer is; that's what I don't get about your point. The C programmer will think of ^x (or alternatively x[0]) as a handle on the string "foo", the same way a good Java programmer would. Some programmers (Java or otherwise) might confuse a handle on "foo" with "foo" itself, but they'll be bitten by that when they try to write a swap function or mutate a string literal or whatever. Java's reference types are restricted pointers that you can only dereference using . or array indexing, you can't use array indexing on any arbitrary reference (it has to be of the right type, but C pointers were already strongly typed), you can only do arithmetic on them via indexing, and you're not allowed to refer to the non-pointer type. None of those differences make them not pointers, to me.

lmm 8y ago
> Well, that's just the little difference I mentioned about C conflating arrays and pointers to them. No, I'm not talking about that at all (I guess I should've used an int rather than a string as an example, but we'd started with ints). I'm talking about the difference between char^ and char^^. > a C programmer is virtually never thinking of 'the address 54fc892d': unless they're doing really low-level stuff, they won't think of it like that any more than a Java programmer, even using pointers all day, just like the Java programmer is; that's what I don't get about your point. The C programmer might think of &x as a handle to x rather than a specific memory address, sure, but they can tell there's a difference between &x and x. The Java programmer doesn't have that distinction to work with. > Java's reference types are restricted pointers that you can only dereference using . or array indexing, you can't use array indexing on any arbitrary reference (it has to be of the right type, but C pointers were already strongly typed), you can only do arithmetic on them via indexing, and you're not allowed to refer to the non-pointer type. None of those differences make them not pointers, to me. I would say: a pointer has to point to something. Java doesn't have those because you can't get talk about "the thing the pointer points to" as a thing distinct from the pointer itself.
- deleted 8y ago
  [deleted]
- deleted 8y ago
  [deleted]
- kbp 8y ago
  > I would say: a pointer has to point to something. Java doesn't have those because you can't get talk about "the thing the pointer points to" as a thing distinct from the pointer itself. You get at the thing being pointed to by dereferencing the pointer. When you copy around handles to it, you can tell that you're only passing around handles, because if the object is mutable, then changes made from one handle show up in others, but your swap function still won't work. All you can do with the handle is pass it around, copy it, compare it to another handle with == or !=, dereference it, and add an index to it before dereferencing it. Dereferencing is specific to pointers, but for all the other things, they behave just like every over Java primitive does. The effect of object variables just being pointers comes up in a lot of places, like "why doesn't my swap function work", using "==" to compare objects, initialising multiple variables to the same instance when you expected copy semantics, etc. These aren't rare things, and they're not difficult to think of. The fact that they're just pointers is the clearest explanation for all of that, and it by itself works for all of that.
  - lmm 8y ago
    > You get at the thing being pointed to by dereferencing the pointer. Which you can't do in Java! There's no * operator. Thinking in terms of pointers does illuminate some of Java's behaviour, sure, but it's not a reasonable way to understand the language when it requires all these concepts from C/C++ that just aren't there in Java.
    - kbp 8y ago
      > > You get at the thing being pointed to by dereferencing the pointer. > Which you can't do in Java! There's no * operator. . and array indexing dereference pointers in Java, just as -> and array indexing do in C. I've already mentioned this several times. > all these concepts from C/C++ that just aren't there in Java. The Java language spec disagrees with you (before you said that explanation was pedantic; now it's incorrect?). As well, C and C++ did not invent pointers; you're the one insisting that Java's pointers aren't pointers because they don't behave identically to C's, I was saying that the specific differences don't change the fact that they're both flavours of pointer. No one is claiming that Java is source-compatible with C. And really, there's no alternative explanation. You can learn each special case individually if you want and let your brain connect the dots to form the notion of how to use a reference without having sat down and thought about it and unified the concept, but that seems like so much work to get around learning a pretty simple idea that fully explains all of it without any special cases.

by kbp 8y ago

lmm 8y ago

> Well, that's just the little difference I mentioned about C conflating arrays and pointers to them. No, I'm not talking about that at all (I guess I should've used an int rather than a string as an example, but we'd started with ints). I'm talking about the difference between char^ and char^^. > a C programmer is virtually never thinking of 'the address 54fc892d': unless they're doing really low-level stuff, they won't think of it like that any more than a Java programmer, even using pointers all day, just like the Java programmer is; that's what I don't get about your point. The C programmer might think of &x as a handle to x rather than a specific memory address, sure, but they can tell there's a difference between &x and x. The Java programmer doesn't have that distinction to work with. > Java's reference types are restricted pointers that you can only dereference using . or array indexing, you can't use array indexing on any arbitrary reference (it has to be of the right type, but C pointers were already strongly typed), you can only do arithmetic on them via indexing, and you're not allowed to refer to the non-pointer type. None of those differences make them not pointers, to me. I would say: a pointer has to point to something. Java doesn't have those because you can't get talk about "the thing the pointer points to" as a thing distinct from the pointer itself.

deleted 8y ago
[deleted]
deleted 8y ago
[deleted]
kbp 8y ago
> I would say: a pointer has to point to something. Java doesn't have those because you can't get talk about "the thing the pointer points to" as a thing distinct from the pointer itself. You get at the thing being pointed to by dereferencing the pointer. When you copy around handles to it, you can tell that you're only passing around handles, because if the object is mutable, then changes made from one handle show up in others, but your swap function still won't work. All you can do with the handle is pass it around, copy it, compare it to another handle with == or !=, dereference it, and add an index to it before dereferencing it. Dereferencing is specific to pointers, but for all the other things, they behave just like every over Java primitive does. The effect of object variables just being pointers comes up in a lot of places, like "why doesn't my swap function work", using "==" to compare objects, initialising multiple variables to the same instance when you expected copy semantics, etc. These aren't rare things, and they're not difficult to think of. The fact that they're just pointers is the clearest explanation for all of that, and it by itself works for all of that.
- lmm 8y ago
  > You get at the thing being pointed to by dereferencing the pointer. Which you can't do in Java! There's no * operator. Thinking in terms of pointers does illuminate some of Java's behaviour, sure, but it's not a reasonable way to understand the language when it requires all these concepts from C/C++ that just aren't there in Java.
  - kbp 8y ago
    > > You get at the thing being pointed to by dereferencing the pointer. > Which you can't do in Java! There's no * operator. . and array indexing dereference pointers in Java, just as -> and array indexing do in C. I've already mentioned this several times. > all these concepts from C/C++ that just aren't there in Java. The Java language spec disagrees with you (before you said that explanation was pedantic; now it's incorrect?). As well, C and C++ did not invent pointers; you're the one insisting that Java's pointers aren't pointers because they don't behave identically to C's, I was saying that the specific differences don't change the fact that they're both flavours of pointer. No one is claiming that Java is source-compatible with C. And really, there's no alternative explanation. You can learn each special case individually if you want and let your brain connect the dots to form the notion of how to use a reference without having sat down and thought about it and unified the concept, but that seems like so much work to get around learning a pretty simple idea that fully explains all of it without any special cases.