CODEWITHSUNDEEP
javamemoryreference
user2029675
user2029675

Reputation: 255

Processing cost of making a new reference to an already-created object?

I'm making a game where I need to tell how many cars are contacting the player's car, and which cars. My plan is to create a List, and add and remove cars when necessary.

Here's my question. My Car class is very expensive to create (processing power wise). How expensive is it to create a reference to a car? I know in C++ what I'm talking about is called a pointer. Here's an example in code:

Car newCar = new Car(); // expensive
Car carCopy = newCar.clone(); // expensive
Car referenceNewCar = newCar; // expensive?

referenceNewCar should point to the same place in memory as newCar, right? So it won't have to initialize anything, and saying newCar.changeMemberVariableTo(1) is the same as referenceNewCar.changeMemberVariableTo(1); either way, newCar and referenceNewCar are both affected, because they point to the same place in memory.

I assume it would be cheaper to create a new reference than an entirely new Car. How much faster is it? If it takes, say, 3 seconds to create a new Car, will creating a new reference to the same car be nearly instantaneous?

Thanks in advance.

Upvotes: 3

Views: 154

Answers (1)

Jon Skeet
Jon Skeet

Reputation: 1500893

Copying a reference from one variable to another is very cheap. It's likely to be as cheap as copying an int or long value (depending on a few things about the JVM in question).

All you've got is two variables with exactly the same value - a reference. That value will be very small (4 or 8 bytes under most implementations) and copying it doesn't usually require any more effort than copying the bytes.

(I've a sneaking suspicion that some JVMs may be a little bit cleverer than this; for the sake of garbage collection, it's possible that some JVMs update flags about the oldest generation which has a reference to a particular object, for example - but that will vary by implementation, and my memory may be wrong anyway.)

Upvotes: 2

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