Java reduce size of object

Question

I'm creating a trie, which my application will hold in it memory. Trie will have a lot of nodes and I'm thinking about how to reduce space usage. Of cause I will use trie to DAWG algorithm to reduse number of nodes, but as far as I know it's not enough.

Here is a node class

class Node{
  char letter;
  boolean EOW; // end of word
  Node child; // first child
  Node next; // next Node on this level
}

As far as I know object of this class will have 14 Bytes (2 Bytes given for char, 4 for boolean variable and 2*4 will be reserved for references)

I think that I can replace char by byte. That will save 1 Byte. However I don't know how much time that will take in type casting. And likely this is a bad desigin.

Also boolean takes 4 Bytes, perhaps you know what I can use instead of boolean?

So I need you to help me reduce size of nodes. Thanks in advance.

Answer 1

If letter takes only 5 bits and eow one bit, you can pack them in a single byte to save memory.

char letter = ...;
boolean eow = ...;

byte packed = (byte) ((eow ? 0b10_0000 : 0) | letter);

letter = (char) (packed & 0b1_1111);
eow = (packed & 0b10_0000) != 0;

Answer 2

If you don't need the weirder half of UTF-16 characters, you can use the highest bit of letter as the EOW marker.

For example, here the eoWletterA variable has the letter 'a' encoded with the EOW bit:

char eoWletterA = 'a' + 0x8000;
char letter = (char) (eoWletterA & 0x7FFF);
boolean eow = BigInteger.valueOf(eoWletterA).testBit(15);

Your trie should be encapsulated properly. Make sure that the EOW bit can't be accidentally set when storing a character to the trie.

UPDATE: Note that removing the boolean variable from the Node may or may not make a difference in the memory footprint of a Node object in a JVM. You can examine the object memory footprint with the following tool: https://stackoverflow.com/a/52682/1207523