'static' can't straightway be blamed for causing memory leaks. But, if the programmer has not well thought the usage and has not taken care of the setting the references to 'null' explicitly after using the static objects then they can definitely cause memory leaks. Let's see how.
As 'static' members will by default live for the entire life of an app unless they are explicitly set to 'null'. So, always make it a point to nullify the references as soon as you reach at a point in your code where the use of the static member is over. For example: suppose you have created a 'Statement' object from a DB Connection and the connection is a pooled one. Now as you know calling close()method on a pooled connection will not actually close the connection instead it will return the Connection object to the pool to be re-used. So, in such a case unless you explicitly close the 'Statement' object, it would keep consuming precious memory space for no real use. Just think the scenario where you have declared the 'Statement' object as a static member, it'll be maintained in the memory for the entire life time of the app even when the control is out of the scope. It's just a sample scenario and many of you might never have used 'Statement' object in such an irresponsible manner. It's just an attempt to show how the 'static' can be misused to cause memory leaks in Java.
Not that if your Statement object is non-static you should reply on the out-of-scope nullification (i.e., as soon as control is out of scope the local objects would be marked for re-claimation) as in case you still have a significant amount of code (in terms of time/space) after using the Statement last and before reaching the end of the local scope, it would be a sheer wastage of memory if you don't explicitly nullify the 'Statement' after its use is over. Such a scenario should also be thought of as memory leaks only and one should always make sure the nullification of resources is as close to their last usage as possible.
Therefore, in summary we can say that one should/must :-
As 'static' members will by default live for the entire life of an app unless they are explicitly set to 'null'. So, always make it a point to nullify the references as soon as you reach at a point in your code where the use of the static member is over. For example: suppose you have created a 'Statement' object from a DB Connection and the connection is a pooled one. Now as you know calling close()method on a pooled connection will not actually close the connection instead it will return the Connection object to the pool to be re-used. So, in such a case unless you explicitly close the 'Statement' object, it would keep consuming precious memory space for no real use. Just think the scenario where you have declared the 'Statement' object as a static member, it'll be maintained in the memory for the entire life time of the app even when the control is out of the scope. It's just a sample scenario and many of you might never have used 'Statement' object in such an irresponsible manner. It's just an attempt to show how the 'static' can be misused to cause memory leaks in Java.
Not that if your Statement object is non-static you should reply on the out-of-scope nullification (i.e., as soon as control is out of scope the local objects would be marked for re-claimation) as in case you still have a significant amount of code (in terms of time/space) after using the Statement last and before reaching the end of the local scope, it would be a sheer wastage of memory if you don't explicitly nullify the 'Statement' after its use is over. Such a scenario should also be thought of as memory leaks only and one should always make sure the nullification of resources is as close to their last usage as possible.
Therefore, in summary we can say that one should/must :-
- always think if you really need to make this variable/member a 'static' one?
- always try to confine the scope of an object to restrict its usage only to the section it's actually needed
- always make a conscious effort to explicitly nullify objects once you finish using them (especially the large objects)
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