I've done some analysis of the size of the backing arrays that are constructed by the RI, by serializing ArrayLists on the RI and then reading them back in on Harmony (the serialization spec saves the length of the backing array). The RI's grow heuristics differ from Harmony in that there's not a minimum grow size - adding an element to a zero capacity ArrayList on the RI grows it by just one element, whereas on Harmony the ArrayList will be grown by a minimum of 12 elements. So this may have an impact if lots of ArrayLists are constructed that only add a few elements. From some experimentation the growth rate on the RI in the general case is to grow by the larger of the size of Collection or 0.5*capacity (and then add 1 if it's the 0.5*capacity!), so: >create an ArrayList and call addAll with 1000 element Collection size is 1000, capacity is 1000 >then call addAll with 1000 element Collection size is 2000, capacity is 2000 >then call addAll with 50 element Collection size is 2050, capacity is 3001 >then call addAll with 1000 element Collection size is 3050, capacity is 4502
On Harmony the growth rate is the larger of the size of the Collection or 0.5*size, so: >create an ArrayList and call addAll with 1000 element Collection size is 1000, capacity is 1000 >then call addAll with 1000 element Collection size is 2000, capacity is 2000 >then call addAll with 50 element Collection size is 2050, capacity is 3000 >then call addAll with 1000 element Collection size is 3050, capacity is 3075 Therefore the arrays will grow at a slower rate on Harmony compared to the RI. I notice a difference between the Java 5 and Java 6 spec for ArrayList in that the requirement that an ArrayList created from a Collection should have capacity 110% of the Collection size has been removed, so maybe we should also remove this from the Java 6 branch of ArrayList. This seems to be the only change between the specs. I also noticed going through the spec that the doc for the add and addAll methods that take a location state that all subsequent elements should be shifted to the right and therefore space should only be added onto the end of the array, and similarly for remove with a location. Currently we try and use both ends of the array, so this is against the spec, but it isn't something that can be tested for (since the backing array isn't accessible and even when it's serialized only the length of the array is stored and not the index of the first element). Cath
