java lang OutOfMemoryError Java heap space

Question

I am getting the following error on execution of a multi-threading program  java lang OutOfMemoryError  Java heap space   The above error occured in one of the threads    Upto my knowledge  Heap space is occupied by instance variables only  If this is correct  then why this error occurred after running fine for sometime as space for instance variables are alloted at the time of object creation  Is there any way to increase the heap space  What changes should I made to my program so that It will grab less heap space

User · Answer

You can get your heap memory size through below programe.

public class GetHeapSize {
    public static void main(String[] args) {
        long heapsize = Runtime.getRuntime().totalMemory();
        System.out.println("heapsize is :: " + heapsize);
    }
}

then accordingly you can increase heap size also by using: java -Xmx2g http://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html

User · Answer

You may want to look at this site to learn more about memory in the JVM  http   developer streamezzo com content learn articles optimization-heap-memory-usage  I have found it useful to use visualgc to watch how the different parts of the memory model is filling up  to determine what to change   It is difficult to determine which part of memory was filled up  hence visualgc  as you may want to just change the part that is having a problem  rather than just say       Fine  I will give 1G of RAM to the JVM    Try to be more precise about what you are doing  in the long run you will probably find the program better for it   To determine where the memory leak may be you can use unit tests for that  by testing what was the memory before the test  and after  and if there is too big a change then you may want to examine it  but  you need to do the check while your test is still running

User · Answer

To avoid that exception  if you are using JUnit and Spring try adding this in every test class    DirtiesContext classMode   DirtiesContext ClassMode AFTER CLASS

User · Answer

Local variables are located on the stack  Heap space is occupied by objects  You can use the -Xmx option  Basically heap space is used up everytime you allocate a new object with new and freed some time after the object is no longer referenced  So make sure that you don t keep references to objects that you no longer need

User · Answer

If you want to increase your heap space  you can use java -Xms lt initial heap size gt  -Xmx lt maximum heap size gt  on the command line  By default  the values are based on the JRE version and system configuration  You can find out more about the VM options on the Java website   However  I would recommend profiling your application to find out why your heap size is being eaten  NetBeans has a very good profiler included with it  I believe it uses the jvisualvm under the hood  With a profiler  you can try to find where many objects are being created  when objects get garbage collected  and more

User · Answer

1 - Yes  but it pretty much refers to the whole memory used by your program      2 - Yes see Java VM options   -Xms lt size gt         set initial Java heap size -Xmx lt size gt         set maximum Java heap size   Ie    java -Xmx2g assign 2 gigabytes of ram as maximum to your app  But you should see if you don t have a memory leak first   3 - It depends on the program  Try spot memory leaks  This question would be to hard to answer   Lately you can profile using JConsole to try to find out where your memory is going to

User · Answer

Upto my knowledge  Heap space is occupied by instance variables only  If this is correct  then why this error occurred after running fine for sometime as space for instance variables are alloted at the time of object creation       That means you are creating more objects in your application over a period of time continuously  New objects will be stored in heap memory and that s the reason for growth in heap memory   Heap not only contains instance variables  It will store all non-primitive data types   Objects   These objects life time may be short  method block  or long  till the object is referenced in your application         Is there any way to increase the heap space       Yes  Have a look at this oracle article for more details   There are two parameters for setting the heap size   -Xms   which sets the initial and minimum heap size  -Xmx   which sets the maximum heap size        What changes should I made to my program so that It will grab less heap space       It depends on your application     Set the maximum heap memory as per your application  requirement Don t cause memory leaks in your application If you find memory leaks in your application  find the root cause with help of profiling tools like MAT  Visual VM   jconsole etc  Once you find the root cause  fix the leaks    Important notes from oracle article     Cause  The detail message Java heap space indicates object could not be allocated in the Java heap  This error does not necessarily imply a memory leak    Possible reasons    Improper configuration   not allocating sufficiant memory  Application is unintentionally holding references to objects and this prevents the objects from being garbage collected Applications that make excessive use of finalizers  If a class has a finalize method  then objects of that type do not have their space reclaimed at garbage collection time  If the finalizer thread cannot keep up  with the finalization queue  then the Java heap could fill up and this type of OutOfMemoryError exception would be thrown     On a different note  use better Garbage collection algorithms   CMS or G1GC   Have a look at this question for understanding G1GC

User · Answer

To increase the heap size you can use the -Xmx argument when starting Java  e g   -Xmx256M

User · Answer

In netbeans  Go to  Run  toolbar  --   Set Project Configuration  --   Customise  --   run  of its popped up windo --   VM Option  --  fill in  -Xms2048m -Xmx2048m   It could solve heap size problem

User · Answer

In most of the cases  the code is not optimized  Release those objects which you think shall not be needed further  Avoid creation of objects in your loop each time  Try to use caches  I don t know how your application is doing  But In programming  one rule of normal life applies as well  Prevention is better than cure   Don t create unnecessary objects

User · Answer

No  I think you are thinking of stack space  Heap space is occupied by objects  The way to increase it is -Xmx256m  replacing the 256 with the amount you need on the command line

[java] java.lang.OutOfMemoryError: Java heap space

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