CODEWITHSUNDEEP
javaarraysperformance
Sophie Sperner
Sophie Sperner

Reputation: 4556

What is faster and less in memory in Java: int[] or boolean[]?

In Java, what is faster and less in memory: int[n] or boolean[n] or maybe Bitset(n) ?

The question is applicable for arrays of small (n is up to 1000), medium (n is between 1000 and 100000) and huge (n is greater than 100000) sizes. Thank you.

I want to achieve flags (1/0) storage.

Upvotes: 1

Views: 3386

Answers (5)

Peter Lawrey
Peter Lawrey

Reputation: 533920

On most JVMs; an array or object has a 12-16 byte overhead. An int use 4 bytes and a boolean uses a byte (it doesn't have to but it does with OpenJDK/HotSpot) BitSet uses two objects and more memory for small sets, but only one bit per have. So for small collections an int[] can be smaller than a BitSet but as the size grows, BitSet will be the smallest.

If the data structure is smaller than your cache the fastest is int[] then boolean[] then BitSet This is because there is non-trival overhead in breaking int into byte or a bit.

However once your cache size becomes important, it can be that the overhead of BitSet fades compared to the overhead of using a slower cache or main memory.

In short: if in doubt use BitSet as this is clearer as to your intent and its likely to be faster.

Upvotes: 3

Puce
Puce

Reputation: 38152

Consider to replace bit flags with enums. Then you can use e.g. EnumSet instead of Bitset.

Upvotes: 0

mishadoff
mishadoff

Reputation: 10789

Actually, it is JVM dependent. For example Sun JVM converts boolean type to int. That mean even boolean variable uses 32 bit. But jvm optimize boolean arrays, and reserve 8 bit per boolean array cell.

Upvotes: 1

Azodious
Azodious

Reputation: 13882

Descending order in memory usage

int[n] > Bitset(n) > boolean[n]

However, in accessing the indexes, there should not be any difference.

Upvotes: 0

J-16 SDiZ
J-16 SDiZ

Reputation: 26930

Java store boolean as int internally. So int[] and boolean[] is exactly the same.

BitSet use less memory. Faster or not depends on your usage pattern.

Upvotes: 0

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