Is there a difference in SIZE between String “a” and a Char 'a'?

Question

Is there a difference in size between a String "a" and a Char 'a'? Should you use a Char when you need to save single letters or numbers?

Answer 1

Note there are actually 3 cases

String "a"
Character 'a'
char 'a'

of these, char 'a' will take up the least amount of space (2 bytes), whereas Char 'a' and String "a" are both objects and so because of the memory overhead associated with an Object, both will be approximately the same size

Answer 2

There is no size difference between a String of one letter and a char of one letter (referring to the backing char array of the String , that is). Currently, they both require 2 bytes as per UTF-16 encoding, but non UTF-16 characters will only require 1 byte once Java 9 is released in July.

The String will obviously use up more memory than the primitive, but it sounds like you're prematurely optimizing.

Answer 3

Let's get something vaguely scientific going on here. I created the following program which creates an array of 100 million characters or strings:

public class NewClass {
    private static final int SIZE = 100000000;

    public static void main(String... args)
    {
        char[] a = new char[SIZE];

        for (int i = 0; i < SIZE; ++i)
        {
            a[i] = 'a';
        }
    }
}

I profiled it once using char[] , once using String[] , and once using Character[] .

The amount of used heap space:

char[]      : 267 million bytes
String[]    : 442 million bytes
Character[] : 437 million bytes

So char is roughly 60% of the size of a 1 character String , which is comparable in size to a Character (on my JVM).