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This question may be a little bit self-explanatory for some of you but I am really trying to understand what are the similarities between: List myList = new ArrayList<Vertex>(); { In JAVA } and Vertex* myList = new Vertex[size] {In C++}. What's the point of that * in C++ that does not exist in Java. I know that it points to the first element of the list..when are we supposed to use *? Is it just for vectors or?

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  • Vertex* myList = new Vertex[size] has been replaced by std::vector<Vertex> myList(size). Sounds like you could use a good C++ book Commented Nov 30, 2018 at 20:07
  • Vertex* myList means that myList is a pointer to a Vertex (because standart C arrays are stored as a pointer to the first element). tutorialspoint.com/cplusplus/cpp_pointers.htm Commented Nov 30, 2018 at 20:12
  • It is a mistake to think that Java ArrayList is like an array. They are two very different things. Commented Nov 30, 2018 at 20:12
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    @AndyTurner I wouldn't say they're so different that comparisons can't be made, but this is definitely a bad example. Still, I think this question is more "What is a pointer?" than a question about arrays. Commented Nov 30, 2018 at 20:14
  • There is an interesting thing in the description of go's type syntax which explains about *: although we tend to write Vertex* myList, the original intent was to write Vertex *myList, to mean that "the type of *myList is Vertex". Since * dereferences a pointer type to its type, this means that myList is a pointer to a Vertex. It's a bit roundabout, but that is, apparently, where the notation arose. Commented Nov 30, 2018 at 20:27

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We cannot talk about similarities/differences when these two languages have different assumptions.

In Java everything is a reference - you are creating objects, they are being stored somewhere (on stack/heap) but you are accessing them only by reference. That means that in myList there will be address kept for the ArrayList instance (real instance - in memory)

In C++ you can access object as objects (with all after-effects like copying whole object when passing as argument to function) but also by reference (using pointers - just to avoid such after-effects but also to use some special gifts given to pointers like iterating over memory cells).

Yeah - about iterating over computer memory - the funny fact in C++ is that it's allocating solid block of memory (I mean - next N cells/addresses in row) to put array there - that's why you can declare your array as

int* a = new int[100]; // this is called dynamic allocation

because what you need is the address of the first element, and the object size (given by pointer type). You can jump to the next element simply by doing

a++

To differ using object/pointer you need (or do not need) asterix operator * and that's why it occurs in C++.

read also What exactly is the purpose of the (asterisk) in pointers?

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Oh alright. But which one is better in C++ then, access by reference or by object?
actually when it comes to arrays you can only access them as pointers - even when you are declaring array as array (I mean int a[100]) it still will be sent to functions and kept under a variable as pointer the the first element - that limitation is because of performance (try to imagine copying 1mln elements on function call). Of course dereffered array element like a[100] or a++ is an object unless you are keeping another pointers in array - why not
Oh so basically whenever I declare an array int a[100] c++ has to copy that for me into a pointer variable int* a which is means extra work?
it does not mean extra work - I'm pretty sure that it's being changed during compilation
I never checked that but really I don't think so

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