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Extension of Colt HashMap using Generics for storage of Objects

This is based on part of the code from Colt Project: The Colt Project is made before generics was introduced in Java. This means that the HashMap from Colt Project cannot be used as a drop-in replacement for Java's HashMap.

This version contains only the HashMap part of Colt Project (version 1.2.0) and adds the support for generics, so that it can now be used as a drop-in replacement for Java's HashHamp


JAR also contains source code

Date Version File Description
22. June 2013 1.01 Benchmark code updated
16. June 2013 1.00 Initial release

Changes to original code

  • Removed all non-hashmap relevant code
  • Fixed bug where OpenLongObjectHashMap.indexOfValue(...) and OpenIntObjectHashMap.indexOfValue(...) used "==" rather than equals for Object types.
  • Created new interfaces and classes for wrapping Colt Project HashMap in Java's Map<K,V> interface.


Class Key type Value type
ColtIntHashMap Int Object
ColtIntIntHashMap Int Int
ColtQuickIntIntHashMap Int Int
ColtIntDoubleHashMap Int Double
ColtLongHashMap Long Object
ColtDoubleIntHashMap Double Int

Existing code can easily be changed to use new HashMaps's. By changing to Colt's HashMap there will be a memory saving because of more efficient storage of keys and possibly values. However the penalty for autoboxing is still present unless using put(...) and get(...) on the native type.

Map<Integer, String> map = new HashMap<Integer,String>();

ColtIntHashMap<String> native = new ColtIntHashMap<String>();
Map<Integer, String> map = native;

//For maximum performance, its necessary to use the original type when putting and retrieving from the map.
//Caveat: When using ColtIntHashMap<Integer> the compiler cannot infer which of the two put methods you want, and you need to use putNative(...) method


JVM options: -Xms8g -Xmx8g Insertions: 20 million (7 million duplicates) get(...) 13 million Contains key: 20 million Removals: 6 million containsValue(): 100

JVM 1.6

Map Memory usage (mb) Insertion get(...) (sec.)
Java HashMap 2485 8 8
Colt HashMap 1711 7 4
Colt (Native) HashMap 1706 6.1 2.6
Colt (IntInt) HashMap 1304 4.7 1.9
Colt (Quick IntInt) HashMap 1304 4.8 1.9