CODEWITHSUNDEEP
javaobjectgarbage-collection
tnaser
tnaser

Reputation: 181

Defining java object inside a loop , do I need to use null to free memory?

If I have a loop and create a new object inside it 

for ( int i ; i < 10 ; i++)
{
  MyObject obj = new MuObject();
   obj.use();
}

Do I need to say obj = null, inside the loop at the beginning or end to release memory used by that object , or by using "new" that object will be send to GC ? and can I see this in terms of memory usage ?

update : so in case I have big object and long loop , should I assign the object to null or no ?

Upvotes: 1

Views: 2080

Answers (4)

seand
seand

Reputation: 5286

Nope, you don't need to set obj to null. When it is reassigned by the next loop iteration the previous reference will be garbage (unless something else points to it) and eligible for cleanup. That's the point of automatic garbage collection.

However there are some cases when you have to watch for things to control memory. If you have an static object pointer set it may never get cleaned up. (it's really not garbage since it has a live reference). One common issue is caches; it may hold unto old stale data that never gets cleaned up.

Upvotes: 1

SutharMonil
SutharMonil

Reputation: 88

As it is even if you call the GC it will not do it immediately, but for good practice you can do so. For memory management you can look into the features of IDE's like netbeans, Eclipse, etc.

Upvotes: 0

Dawood
Dawood

Reputation: 5306

Check this: http://javarevisited.blogspot.com/2011/04/garbage-collection-in-java.html

"An Object becomes eligible for Garbage collection or GC if its not reachable from any live threads or any static references". After the loop ends, the objects that you created inside the loop do not have any external references pointing to them and are eligible for garbage collection.

EDIT:
If you want to see memory usage, you can profile your application using an IDE that has such a feature. For example, NetBeans has a nice interface that shows live memory usage for object allocation.

EDIT 2:
"so in case I have big object and long loop , should I assign the object to null or no ?"
No, you do not need to do this. Once one iteration of the loop is complete, there are no active references to any objects created in that iteration so it does not matter that you have a long or short loop.

Upvotes: 7

Yann Ramin
Yann Ramin

Reputation: 33177

Do I need to say obj = null, inside the loop at the beginning or end to release memory used by that object , or by using "new" that object will be send to GC ?

Neither, really. new only constructs new objects. When there are no references to the object, such as falling out of scope (i.e., not in the loop block), it will be eligible for garbage collection. Note that Java's garbage collector does not immediately collect objects - it does it in batches when it feels that it is required.

and can I see this in terms of memory usage ?

I would suggest looking at VisualVM, including with your JDK. It has a memory view, and a garbage collector view through a plugin.

Note that you cannot rely on the operating system "in use" count - the Java heap will rarely shrink especially if there aren't any major collections.

Upvotes: 1

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