Round to digits

[KillCloud]

Please tell me how to round a number to digits, like round 1.345666 to 2 digits, thus, 1.35.

[KillCloud]

Ok i know that

code:

System.out.printf("%.2f", someNumber);

will round to 2 decimal place but i dont understand how it works
can someone explain it? thx

[Andy]

why not look it up on the [url=http://java.sun.com/j2se/1.5.0/docs/api/java/io/PrintStream.html#printf(java.lang.String,%20java.lang.Object...)]java[/url] api?

[ericfourfour]

Or you can make your own method. Here;s how it could look.

code:

int mult_by = 10 ^ decimal_places int rounded = (int) (num * mult_by + 0.5) double new_num = rounded / (mult_by * 1.0)

I'm pretty sure that should work.

[zylum]

you could do a little bit better:

code:

double mult_by = Math.pow(10, decimal_places); double rounded = Math.round (num * mult_by); double new_num = rounded /mult_by;

*note this is untested but you get the point.. ei use the round() method rather than adding 0.5 and casting. also, if you are dealing with 2 ints and you are dividing and you want to keep decimal places, cast one of the ints to a double rather than multiply by 1.0

[ericfourfour]

another improvement would be:

code:

double mult_by = 1edecimal_places

That one can use negatives to you could round to negative decimals.
For example:
num = round (127, -2)
num would equal 100 (or 130 I can't think right now).

[ericfourfour]

This one should work. I added 0.5 and casted to an integer because that way it isn't dependant on Math.round (using a separate rounding method for your rounding method doesn't make much sense). I also threw in a power method because the one in the Math class doesn't do negatives. This one has been tested and it works.

code:

public static double power (double base, int exponent) {     if (exponent < 0) return power (base, exponent + 1) / base;     else if (exponent > 0) return power (base, exponent - 1) * base;     return 1; }     public static double round (double num, int decimal_places) {     double mult_by = power (10, decimal_places);     double rounded = (int) (num * mult_by + 0.5);     return rounded / mult_by; }

code:

System.out.println (round (1251.345, -1)); Output: 1250.0 System.out.println (round (1251.345, 2)); Output: 1251.35 System.out.println (round (1251.345, 0)); Output: 1251.0

[Ultrahex]

Im Hoping You guys know that there is something called DECIMAL FORMATTING in java...... oh well lol

[Aziz]

Guys, don't reinvent the wheel:

Math.round() will return a long type rounded to the nearest 1.
Math.pow(double x, double y) will return x^y

To round to 2 decimal places...

Java:

int x = 2.6666666666; x = (int) (Math.round(x * 100) / 100);

Or, a simple function:

Java:

public long roundTo(double x, int places) {   return Math.round(x * Math.pow(10, places)) / Math.pow(10, places' }

That way, you can round to the nearest hundred (so 155 will be 200) by specifying -3 as the 'places'. Or something like that. No time to test it out, I'm at school.