Meaning of 0_0 in Java 7

Question

I have read that in Java7, we can now write this funny statement :

public static boolean isZero(int O_O){
  return O_O == 0_0;
}

The question is : What exactly does 0_0 mean in this context ?

http://docs.oracle.com/javase/7/docs/technotes/guides/language/underscores-literals.html — Colin D, Jul 29 '13 at 16:45
I'm getting flashbacks to Fortran which allowed spaces in numbers for "readability" — Dale Wilson, Jul 29 '13 at 16:46
@Colin Yes, and it obvisouly works. I was actually wondering what was the semantic difference between 0 and 0_0. According to the answers, it seems to only be a question of readability. — Arnaud Denoyelle, Jul 29 '13 at 16:47
@arshajii: `0_8` is a compiler error ;) So that shouldn't be a problem... — jlordo, Jul 29 '13 at 17:30
@jlordo Yes, that's my point. `0_0` is really an octal int literal. — arshajii, Jul 29 '13 at 17:31
@arshajii: Ok, a better example would be `0_12 != 12`, as it would at least compile ;) — jlordo, Jul 29 '13 at 17:37

score 42 · Accepted Answer · answered Jul 29 '13 at 16:43

42

Underscore characters in numerical literals are allowed in Java 7 just for the readibility purpose. From the javadocs:

In Java SE 7 and later, any number of underscore characters (_) can appear anywhere between digits in a numerical literal. This feature enables you, for example, to separate groups of digits in numeric literals, which can improve the readability of your code

answered Jul 29 '13 at 16:43

Juned Ahsan

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Wow, look at that number climb! – Reinstate Monica -- notmaynard Jul 29 '13 at 16:45
O what the heck! +1 from me X_X – Bart Jul 29 '13 at 16:47
When I see a number climb I cannot resist contributing – arynaq Jul 29 '13 at 16:51

jlordo · Answer 2 · 2013-07-29T17:25:49.247

15

In Java 7 you can add underscores to increase the readability of number literals:

int oldMillion = 1000000;
int newMillion = 1_000_000;

It's especially useful with binary data:

byte oldMax = 0b01111111;
byte newMax = 0b0111_1111;

edited Jul 29 '13 at 17:25

answered Jul 29 '13 at 16:44

jlordo

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nanofarad · Answer 3 · 2013-08-15T11:52:58.550

Underscores are valid in numbers as long as they aren't the first character, last character, or directly on either side of 0x, 0b¹, etc. Basically between digits.

For example, 4_294_967_296 is a more standard use of this.

Your code will check if the int passed is equal to zero.

However, this is not a decimal int, but rather, an octal int. 0_12 does not equal 12 or 1_2. Instead, the former is equal to 10 in decimal.

¹ Binary literals were added in Java 1.7.

Meaning of 0_0 in Java 7

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