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Thread: Omitting local large variable to save memory

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    Default Omitting local large variable to save memory

    Hi all,

    I have a question regarding best practice in using local variables as my method return variable.

    I have a method like this

    myReturnObject getMyObject(String input) {
          myReturnObject myObject = null;
          try {
             myObject = helperObject.someOtherMethod().getObject(input); //getObject has return type myReturnObject
          } catch (Exception e) {
             //log any problems
          }
          return myObject;
    }

    And I'm wondering if I rewrite like this if I'll see some performance optimization benefit

    myReturnObject getMyObject(String input) {
          try {
             return helperObject.someOtherMethod().getObject(input); //getObject has return type myReturnObject
          } catch (Exception e) {
             //log any problems
          }
          return null;
    }

    myObject can be quite large -- so I'm wondering if I can omit the myReturnObject local variable instance if it'll save some work from the garbage collector.

    I welcome your input!

    Thanks,

    -Wolf


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    Default Re: Omitting local large variable to save memory

    What happened when you tried this and did some profiling?
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    Default Re: Omitting local large variable to save memory

    Once the local variable myObject goes out of scope it will not be reachable by any other object, and thus will be available for garbage collection. However, the question is will that local variable take up more resources? In most VMs I am aware of, it will. But probably not as much as we might think; that reference is still stored thread-local and still takes up some resources. But this will depend on the VM.

    The code changes, too, so the execution profile and compile size might change. The latter is easy to check with javap.

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    Default Re: Omitting local large variable to save memory

    A variable does not really need much memory. Those are only a few bytes since it is merely a pointer. Its the object itself that needs memory, and since you do not create a new object you will also not need much memory.

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    Default Re: Omitting local large variable to save memory

    Quote Originally Posted by Cornix View Post
    A variable does not really need much memory. Those are only a few bytes since it is merely a pointer. Its the object itself that needs memory, and since you do not create a new object you will also not need much memory.
    That said, when I'm in another thread and assign the return value to yet another variable then I don't need to worry about the object being held in memory twice?

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    Default Re: Omitting local large variable to save memory

    Nope. An object exists exactly once in memory. Variables are just references to the position in memory (or in the case of java in heap space) at which the object exists.

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