Over a million developers have joined DZone.

Size of an entry in a Map

· Java Zone

Check out this 8-step guide to see how you can increase your productivity by skipping slow application redeploys and by implementing application profiling, as you code! Brought to you in partnership with ZeroTurnaround.

There have been some very good articles on the size of a map. However as a map grows, it initial size become less important and the size per entry is what matters.

How are the sizes measured

In these tests an int key and long values are used. This adds a small but realistic size to each entry.

Size per entry of a medium sized Map

The following are the size per entry in bytes. The Map has 1024 entries.

Type of Map 32-bit 64-bit compressed 64-bit not compressed
TIntLongHashMap 26.9 26.9 27.0
FastMap (recycled) 32.0 39.9 47.9
IdentityHashMap 48.0 56.0 80.0
ConcurrentSkipListMap 68.3 76.1 108.3
TreeMap 64.0 80.0 112.0
HashMap 64.0 80.0 112.0
SynchronizedMap 64.0 80.0 112.0
ConcurrentHashMap 65.2 81.4 114.0
Properties 68.0 84.0 120.0
Hashtable 68.0 84.0 120.0
LinkedHashMap 72.0 88.0 128.1
WeakHashMap 80.0 88.0 136.1
 
The Javolution FastMap needed to be recycled. If it is not recycled, it was the largest per entry.

Conclusion

It may be worth considering The GNU Trove collections if you have primitive keys and/or values. However if you have non-trivial keys or values classes, the size of the collection is less likely to matter.

The Code

SizeOfMapsTest.java

 

From http://vanillajava.blogspot.com/2011/07/size-of-entry-in-map.html

The Java Zone is brought to you in partnership with ZeroTurnaround. Check out this 8-step guide to see how you can increase your productivity by skipping slow application redeploys and by implementing application profiling, as you code!

Topics:

Opinions expressed by DZone contributors are their own.

The best of DZone straight to your inbox.

SEE AN EXAMPLE
Please provide a valid email address.

Thanks for subscribing!

Awesome! Check your inbox to verify your email so you can start receiving the latest in tech news and resources.
Subscribe

{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}