Question

I am bit confused about how Java handle conversion.

I have char array consist of 0 (not ‘0’)

char[] bar = {0, 'a', 'b'};
System.out.println(String.valueOf(bar));

When this happens println method does not output anything. But when I treat zero as character:

char[] bar = {'0', 'a', 'b'};
System.out.println(String.valueOf(bar));

Then it output “0ab” as expected.

My understanding was if you declare array of primitive type with empty value like:

char[] foo = new char[10];

those empty cells have default value of 0 in Java, so I thought it was ok to have 0 in the char array but seems like not. Could anyone explain why print method is not even outputting ‘a’ and ‘b’ ?

Answer 1

As you have discovered, the character value of the integer 0 and the character literal '0' are different. To convert a number to the character representation of a decimal digit, you need to do something like this:

int digit = ... // some value between 0 and 9
char ch = (char)(digit + '0');

You can also do this as:

int digit = ... 
char ch = Character.forDigit(digit, radix);

where radix has a value between Character.MIN_RADIX and Character.MAX_RADIX. A radix of 10 gives you a decimal digit. See Character.forDigit(int,int).

The character value zero is the Unicode codepoint NULL (0x0000). This is a non-displayable “control character”. If you try to display it, you are liable to see either nothing at all (as you are getting) or a special glyph that means “I cannot display this character”.