Ecosyste.ms: Awesome
An open API service indexing awesome lists of open source software.
https://github.com/vlsi/compactmap
Memory efficient java.util.Map implementation modelled after http://code.google.com/apis/v8/design.html
https://github.com/vlsi/compactmap
Last synced: 2 days ago
JSON representation
Memory efficient java.util.Map implementation modelled after http://code.google.com/apis/v8/design.html
- Host: GitHub
- URL: https://github.com/vlsi/compactmap
- Owner: vlsi
- License: apache-2.0
- Created: 2011-06-09T06:15:03.000Z (over 13 years ago)
- Default Branch: master
- Last Pushed: 2024-02-14T15:05:25.000Z (8 months ago)
- Last Synced: 2024-04-16T19:01:58.725Z (6 months ago)
- Language: Java
- Size: 75.2 KB
- Stars: 59
- Watchers: 5
- Forks: 6
- Open Issues: 1
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
[](https://travis-ci.org/vlsi/compactmap)
[](https://maven-badges.herokuapp.com/maven-central/com.github.vlsi.compactmap/compactmap)
CompactHashMap
==============
Usage
-----
Add Maven dependency:
```xml
com.github.vlsi.compactmap
compactmap
1.3.0
```
Gradle:
```kotlin
compile("com.github.vlsi.compactmap:compactmap:1.3.0")
```
About
-----
This is a memory efficient alternative to HashMap.
Main design goal is taken from "Fast Property Access"
http://code.google.com/apis/v8/design.html#prop_access.
This implementation however can store specific key-value pairs out of the map,
so they do not consume memory when repeated in different maps.
The expected memory consumption (8u40, 64 bit, compressed references) is as follows:
# of elements CompactHashMap HashMap (with 1.0 fillFactor)
0 32 48
1 32 104
2 32 136
3 32 176
4 64 208
5 64 256
6 64 288
7 72 320
8 72 352
In other words, the first three non default values consume the same
32 bytes, then map grows as 32 + 16 + 4 * (n-2) == 40 + 4 * n.
Regular HashMap grows as 64 + 36 * n.
The runtime of put and get is constant.
The expected runtime is as follows (measured in hashmap and array accesses):
best case worst case
get 1 hashmap + 1 array 2 hashmap
put 1 hashmap + 1 array 6 hashmap
Sample
------
``` java
// Mark height->auto a default mapping entry, so it would not consume memory in CompactHashMaps
CompactHashMapDefaultValues.add("height", "auto");
// Mark all values of width as default, so they would not consume memory in real maps
CompactHashMapDefaultValues.add("width");
CompactHashMap map = new CompactHashMap();
map.put("height", "auto"); // does not consume memory in map
map.put("width", "100%"); // does not consume memory in map either
map.put("id", "myFirstButton"); // consumes some memory
map.get("height"); // => "auto"
map.get("width"); // => "100%"
map.get("id"); // => "myFirstButton"
map.put("height", "50px"); // consumes some memory (switches from default to custom)
map.get("height"); // => "50px"
```
License
-------
This library is distibuted under terms of Apache 2.0 License, see https://raw.githubusercontent.com/vlsi/compactmap/master/LICENSE
Change log
----------
v2.0:
* Change license: LGPL 2.0 -> Apache-2.0
v1.3.0
* Improvement: implement null keys
* Improvement: `Map#toString`
* Improvement: `Map#hashCode` + `equals`
* Improvement: `Map.Entry#hashCode` + `equals`
* Improvement: `Map.Entry#toString`
* Improvement: `Map#containsValue` (it is slow but it works)
* Test: use `guava-testlib` for `Map` implementation testing
v1.2.1
* Improvement: release to Maven Central
* Improvement: fix EntrySet.remove method
v1.2.0
* Improvement: reduce size of hidden classes by using persistent dexx-collections.
* Improvement: mavenize build
* Switch to semantic versioning
v1.1
* Fix: #1 containKey returns true on non existing key
* Fix: #2 size should account removed keys
* Improvement: #3 Default values should be serialized as map
Author
------
Vladimir Sitnikov