A little minibechmark about Map with define size and witout it

The problem you have is you are creating lots of objects, triggering lots of GCs and this is slowing your down, but in a random way.

If you perform a System.gc() at the start of each test and increase the size of the young generation to say 1 GB, you can get this

testHashMapWithoutSize:258testHashMapWithoutSize:177testHashMapWithoutSize:158testHashMapWithoutSize:153testHashMapWithoutSize:152testHashMapWithoutSize:151testHashMapWithoutSize:152testHashMapWithoutSize:150testHashMapWithoutSize:158testHashMapWithoutSize:152testHashMapWithSize:89testHashMapWithSize:80testHashMapWithSize:81testHashMapWithSize:85testHashMapWithSize:80testHashMapWithSize:79testHashMapWithSize:87testHashMapWithSize:80testHashMapWithSize:81testHashMapWithSize:86

where the tests are run with the options -Xmn1g -Xmx2g and you have

public void testHashMapWihtoutSize(int size) { System.gc(); // before each test to reduce the impact of the GC.

In reality you will get GCs in real programs but this helps show you what the problem is.

EDIT In the same test you can do this

public void testTIntObjectHashMapWithSize(int size) { System.gc(); String var = "asdf43trsdg345t"; long ts = System.currentTimeMillis(); TIntObjectHashMap map = new TIntObjectHashMap(size*3/2); for (int i = 0; i < size; i++) { map.put(i, var); } System.out.println("testTIntObjectHashMapWithSize:" + (System.currentTimeMillis() - ts));}public void testMyIntObjectMapWithSize(int size) { System.gc(); String var = "asdf43trsdg345t"; long ts = System.currentTimeMillis(); MyIntObjectMap map = new MyIntObjectMap(size); for (int i = 0; i < size; i++) { map.put(i, var); } System.out.println("testMyIntObjectMapWithSize:" + (System.currentTimeMillis() - ts));}static class MyIntObjectMap { private T[] values; MyIntObjectMap(int size) { values = (T[]) new Object[size]; } public void put(int i, T var) { values[i] = var; }}public static void main(String[] args) { Bechmarking bech = new Bechmarking(); int size = 5000000; for (int i = 0; i < 10; i++) { bech.testHashMapWihtoutSize(size); bech.testHashMapWithSize(size); bech.testTIntObjectHashMapWithSize(size); bech.testMyIntObjectMapWithSize(size); }}

prints

testHashMapWithoutSize:155testHashMapWithSize:77testTIntObjectHashMapWithSize:57testMyIntObjectMapWithSize:8testHashMapWithoutSize:157testHashMapWithSize:78testTIntObjectHashMapWithSize:56testMyIntObjectMapWithSize:7testHashMapWithoutSize:161testHashMapWithSize:79testTIntObjectHashMapWithSize:57testMyIntObjectMapWithSize:7testHashMapWithoutSize:157testHashMapWithSize:78testTIntObjectHashMapWithSize:58testMyIntObjectMapWithSize:7

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