How does memory allocation of an ArrayList work?

Question

As far as I know, when we are creating an ArrayList:

ArrayList list = new ArrayList(SIZE);

The JVM res

Answer 1

This will throw an OutOfMemoryError as soon as there is not enough heap space to allocate the new array.

Garbage collection will always be done before this error is thrown. This will compact memory and eliminate all the arrays of smaller sizes that are no longer used. But there is no way to get around the fact that the old array, the new array, and all the contained objects need to all be in memory at once in order for the old contents to be copied into the new list.

So, if your memory limit is 10 MB, and the array takes up 2 MB and is being sized up to 3 MB, and the strings take up 6 MB, then OOM will be thrown even though after this operation you will only have 3 + 6 = 9 MB in memory. One way to avoid this, if you want to run really close to memory limits with a huge array, is to size the array to the full size to begin with so that it never needs to resize.