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

Answer 1

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.