Java heap space out of memory?

There are a variety of tools that you can use to help diagnose this problem. The JDK includes JVisualVM that will allow you to attach to your running process and show what objects might be growing out of control. Netbeans has a wrapper around it that works fairly well.

Eclipse has the Eclipse Memory Analyzer which is the one I use most often, just seems to handle large dump files a bit better. There's also a command line option, -XX:-HeapDumpOnOutOfMemoryError that will give you a file that is basically a snapshot of your process memory when your program crashed. You can use any of the above mentioned tools to look at it, it can really help a lot when diagnosing these sort of problems Depending on how hard the program is working, it may be a simple case of the JVM not knowing when a good time to garbage collect may be, you might also look into the parallel garbage collection options as well.

There are a variety of tools that you can use to help diagnose this problem. The JDK includes JVisualVM that will allow you to attach to your running process and show what objects might be growing out of control. Netbeans has a wrapper around it that works fairly well.

Eclipse has the Eclipse Memory Analyzer which is the one I use most often, just seems to handle large dump files a bit better. There's also a command line option, -XX:-HeapDumpOnOutOfMemoryError that will give you a file that is basically a snapshot of your process memory when your program crashed. You can use any of the above mentioned tools to look at it, it can really help a lot when diagnosing these sort of problems.

Depending on how hard the program is working, it may be a simple case of the JVM not knowing when a good time to garbage collect may be, you might also look into the parallel garbage collection options as well.

Oracle. Com/technetwork/java/javase/clopts-139448. Html#gbzrr – Eli Acherkan Jul 19 at 20:03 Could be, It was a different, though similar page from the same company that I copied my text from.

Thanks for the correction – mezmo Jul 19 at 21:42.

Java is supposed to clear the heap space for you when all of the objects are no longer referenced. It won't generally release it back to the OS though, it will keep that memory for it's own internal reuse. Maybe check to see if you have some arrays which are not being cleared or something.

Try adding -Xmx for more memory ( java -Xmx1024M YourClass ), and don't forget to stop referencing variables you don't need any more (memory leaks).

No. The heap is cleared by the garbage collector whenever it feels like it. You can ask it to run (with System.gc()) but it is not guaranteed to run.

First try increasing the memory by setting -Xmx256m.

There is no way to dynamically increase the heap programatically since the heap is allocated when the Java Virtual Machine is started. However, you can use this command java -Xmx1024M YourClass to set the memory to 1024 or, you can set a min max java -Xms256m -Xmx1024m YourClassNameHere.

If so, you have a memory leak. You just need to find where that is happening and make sure that you remove the references to the variables when they are no longer needed (this would automatically happen if they go out of scope). If you actually need all that data from previous simulations in memory, you need to increase the heap size or change your algorithm.

If you are using a lot of memory and facing memory leaks, then you might want to check if you are using a large number of ArrayLists or HashMaps with many elements each. An ArrayList is implemented as a dynamic array. The source code from Sun/Oracle shows that when a new element is inserted into a full ArrayList, a new array of 1.5 times the size of the original array is created, and the elements copied over.

What this means is that you could be wasting up to 50% of the space in each ArrayList you use, unless you call its trimToSize method. Or better still, if you know the number of elements you are going to insert before hand, then call the constructor with the initial capacity as its argument. I did not examine the source code for HashMap very carefully, but at a first glance it appears that the array length in each HashMap must be a power of two, making it another implementation of a dynamic array.

Note that HashSet is essentially a wrapper around HashMap.

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