Memory reservation for java objects

I know that when declaring object instances in c++ like so:

Object object

the Object constructor is called and memory is provided for that object, however i find that when you do this in java the object instance doesn't have a value until:

object = new Object()

is written. I want to know specifically when memory is provided for the object. I thought that both construction and the new keyword allocated memory so Object object = new Object() seems redundant. I read on oracle's site that declaration "reserves" memory and new "allocates" memory, I would like to know what is the difference between the two.

Jon Skeet
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You need to differentiate between the space required for the variable and the space required for the object. Bear in mind that the value of the variable is just a reference - very much like a pointer in C++. So if you have:

Object x = null;

then the variable x itself takes up enough space for a reference (usually 4 or 8 bytes). Now if you have:

x = new Object();

that creates an object - the value of x is now a reference to the newly created object. x itself takes up the same amount of space as before, but there's also the space required for the object itself (basically the fields, a reference for the type of the object, and data for synchronization and house-keeping).

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