Basic Object Oriented Pointer Question

[mortal prawn]

This is just a basic question. I don't really understand why in the context of this code the generic variable "Item" doesn't become a pointer shared to the same address the array points to.

The code:

public T pop(){
    T item = stack[size]; // stack is an array of type T
    stack[size] = null;
    return item;
}

(No exceptions are thrown- code compiles and runs successfully)

[frail pendant]

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[mortal prawn]

for clarification, I thought this would happen:

and then when the array location is set to null I assumed null would be returned

This is what seems to actually happen:

[stable blade]

stack[size] = something doesn't modify the object contained in stack[size]
It puts another object (or here, the null pointer) in stack[size]

As usual

If you want to modify the object in stack[size] you need to do something of these sorts:

stack[size].stuff = thingy;

stack[size].incrementSomething();

[inland fable]

What really happens is you change what object an element of an array points to, but not move or delete it in any way! Arrays do not store objects themselves but only references to them

You expect item variable to be a pointer to a pointer to an object (T**), so, if you change to the original pointer, the other one will also point to null, but that's not true. Java variables can only store pointers directly to objects, therefore changing value of one of the pointers won't affect the rest.

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[mortal prawn]

Thank you both!

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