thekeenant / java-primitives-vs-objects

int[] and Integer experiments

jprimitives

A simple library, but more for me to experiment with int vs Integer and other primitives in Java. Unfortunately, at this time Java does not support primitives in generics, such as List<int> like you might use in C# (a resizable int[]).

When performance is critical, it's important to use primitive arrays in order to minimize cache misses due to internal fragmentation of your data. Below are comparisions of int[] and ArrayList<Integer> sorting on the same collection of 1..n ints/integers.

Tests

int[] quicksort vs ArrayList<Integer> mergesort:

Preparing 10 elements...
	0ms (int[])
	0ms (ArrayList<Integer>)
Preparing 100 elements...
	0ms (int[])
	0ms (ArrayList<Integer>)
Preparing 1000 elements...
	0ms (int[])
	1ms (ArrayList<Integer>)
Preparing 10000 elements...
	1ms (int[])
	6ms (ArrayList<Integer>)
Preparing 50000 elements...
	3ms (int[])
	22ms (ArrayList<Integer>)
Preparing 100000 elements...
	9ms (int[])
	31ms (ArrayList<Integer>)
Preparing 1000000 elements...
	91ms (int[])
	343ms (ArrayList<Integer>)
Preparing 10000000 elements...
	925ms (int[])
	2854ms (ArrayList<Integer>)

int[] mergesort vs ArrayList<Integer> mergesort:

Preparing 10 elements...
	0ms (int[])
	0ms (ArrayList<Integer>)
Preparing 100 elements...
	0ms (int[])
	0ms (ArrayList<Integer>)
Preparing 1000 elements...
	0ms (int[])
	1ms (ArrayList<Integer>)
Preparing 10000 elements...
	1ms (int[])
	7ms (ArrayList<Integer>)
Preparing 50000 elements...
	6ms (int[])
	20ms (ArrayList<Integer>)
Preparing 100000 elements...
	15ms (int[])
	28ms (ArrayList<Integer>)
Preparing 1000000 elements...
	156ms (int[])
	239ms (ArrayList<Integer>)
Preparing 10000000 elements...
	1432ms (int[])
	2960ms (ArrayList<Integer>)

A fluent API for Comparator implementations was added in Java 8 that allows convenient methods for creating a relatively complex or multi-part sorting algorithm:

Comparator.nullsFirst(String.CASE_INSENSITIVE_ORDER).thenComparing(str -> {
  // ...
}, (s1, s2) -> ...).reversed();

Again, thanks to generics, any attempt to use this API for sorting primitives requires the usage of the wrapper class. This could be solved by primitive comparators, lists, and more:

Examples:

• IntComparator: maintains a similar fluent API as Comparator but accepts and outputs only IntComparator instances. This comparator would then be accepts as a parameter in Arrays.sort(int[], comparator).
• IntArrayList: similar API as ArrayList but maintains an int[] as opposed to the wrapper Integer[] class.