Assigning “null” to objects in every application after their use

Question

• Do you always assign null to an object after its scope has been reached?

• Or do you rely on the JVM for garbage collection?

Answer 1

- Do you always assign null to an object after its scope has been reached?

No

- Or do you rely on the JVM for garbage collection?

Yes

- Do you do it for all sort of applications regardless of their length?

Yes

- If so, is it always a good practice?

N/A

Answer 2

I assume you're asking this question because you've seen code with variables being assigned to null at the point where they will never be accessed again.

I dislike this style, but another programmer used it extensively, and said he was taught to do so at a programming course at his university. The reasoning he gave is that it would prevent undetectable bugs if he tried to reuse the variable later on, instead of indeterminate behavior, he'd get a null pointer exception.

So if you're prone to using variables where you shouldn't be using variables, it might make your code more easy to debug.

Answer 3

The one time I tend to use this practice is if I need to transform a large Collection in some early part of a method.

For example:

public void foo() {
  List<? extends Trade> trades = loadTrades();
  Map<Date, List<? extends Trade>> tradesByDate = groupTradesByDate(trades);
  trades = null; // trades no longer required.

  // Apply business logic to tradesByDate map.
}

Obviously I could reduce the need for this by refactoring this into another method: Map<Date, List<? extends Trade>>> loadTradesAndGroupByDate() so it really depends on circumstances / clarity of code.

Answer 4

When using the .Net I don't think there's a need to set the object to null. Just let the garbage collection happen.

Answer 5

It's not necessary to explicitly mark objects as null unless you have a very specific reason. Furthermore, I've never seen an application that marks all objects as null when they are no longer needed. The main benefit of garbage collection is the intrinsic memory management.

Answer 6

• no, don't do that, except for specific cases such as static fields or when you know a variable/field lives a lot longer than the code referencing it
• yes, but with a working knowledge of your VM's limits (and how to cause blocks of memory to be held accidentally)
• n/a