How to round a number to within a certain range?

问题

I have a value like this:

421.18834

And I have to round it mathematical correctly with a mask which can look like this:

0.05
0.04
0.1

For example, if the mask is 0.04, i have to get the value 421.20, because .18 is nearer at .20 than .16.

All functions that I found using Google didn't work.

Can you please help me?

回答1:

double initial = 421.18834;
double range = 0.04;

int factor = Math.round(initial / range); // 10530 - will round to correct value

double result = factor * range; // 421.20

回答2:

You don't need a special function. You multiply your original number by (1/mask), you round it to a decimal and you divide again by the same factor.

Example with 0.05

factor = 1/0.05 = 20
421.18834 * 20 =  8423.7668
int(  8423.7668 ) = 8424
8424.0 / 20.0 = 421.20

Example with 0.01

factor = 1/0.1 = 10
421.18834 * 10 = 4211.8834
int( 4211.8834 ) = 4212
4212.0 / 10.0 = 421.20

回答3:

Both fredley and Matteo make the assumption that the rounding factor is itself a factor of 100. For factors like 0.06 or 0.07, this is an incorrect assumption.

Here's my Java routine:

public double rounded(double number, double factor) {
    long integer = (long) number;
    double fraction = number - integer;
    double multiple = (fraction / factor);
    multiple = Math.round(multiple);
    return factor * multiple + integer;
}

回答4:

Contrary to all the answers you will probably get here about multiplying and dividing, you can't do this accurately because floating point doesn't have decimal places. To need to convert to a decimal radix and then round. BigDecimal does that.

来源：https://stackoverflow.com/questions/7851492/how-to-round-a-number-to-within-a-certain-range

标签

java

rounding