Heap space out of memory

Question

My application currently consumes quite a lot of memory because it is running physics simulations. The issue is that consistently, at the 51st simulation, Java will throw an error usually because of a heap space out of memory (my program eventually runs thousands of simulations).

Is there anyway I can not just increase the heap space but modify my program so that the heap space is cleared after every run so that I can run an arbitrary number of simulations?

Edit: Thanks guys. Turns out the simulator software wasn't clearing the information after every run and I had those runs all stored in an ArrayList.

Answer 1

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 

Answer 2

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.