What does influence the most on the time of creating an object?

Question

I know that creating an object takes time and that's why the flyweight pattern exists. What I would like to know is what increases the time of creating a single object the most?

I thought it might be the search of the a slightly larger space in the memory, but I guess it is only slightly larger than each of the fields the object has. Then maybe it is the travel to the correct address in the memory while we are looking for a value of a specific field, but then again: the only thing we added is looking for the address of the object.

Answer 1

There are 3 ways object creation is costly:

1) the object allocation. This is actually pretty cheap (like some nanos), however take into account that

• many objects have "embedded" objects which are implicitely also allocated and

• Additionally often the time of the constructor running (initializing the object) is more costly than the actual allocation.

2) any allocation consumes Eden space, so the higher the allocation rate, the more CPU is consumed by GC (NewGen GC runs more frequent)

3) CPU caches. If you allocate temporary objects (e.g. Integer when putting to HashMap, those temp objects are are put in the L1 cache evicting some other data. If you use it only once, this does not payoff. Therefore high allocation rate (especially temporarys/immutables) lead to cache misses, causing significant slowdown in case (depending on what the app is actually trying to achieve).

Another issue is life cycle. The VM can handle best short lived or very long lived objects. If your application creates a lot of middle-age-dying objects (e.g. cache's), you will get more frequent Full GC's.

Regarding flyweight patterns. It depends. If its a very smallish object, flyweight frequently will not pay off. However if your usage patterns involves many allocations of the flyweight candidate obejct, flyweight'ing will pay off. That's the reason hotspot caches 10.000 Integer objects internally by default

Answer 2

In modern JVMs the object creation is not as costly as it were. It mostly needs to bump the pointer. In fact, in modern JVMs, many objects are actually secretly allocated on the machine stack, and that's basically free- it takes no time at all.

And regarding flyweight pattern: flyweight pattern is not used as the object creation is costly rather it is used to minimize memory use by sharing as much data as possible with other similar objects.