How to round *down* integers in Java?

Question

I'd like to round integers down to their nearest 1000 in Java.

So for example:

• 13,623 rounds to 13,000
• 18,999 rounds to 18,000
• etc

Answer 1

Simply divide by 1000 to lose the digits that are not interesting to you, and multiply by 1000:

i = i/1000 * 1000

Or, you can also try:

i = i - (i % 1000)

Answer 2

You could divide the number by 1000, apply Math.floor, multiply by 1000 and cast back to integer.

Answer 3

int i = Math.floorDiv(-13623, 1000) * 1000 
//i => -14000

The above code will always round down (towards negative infinity) assuming the divisor (1000 in the example) is positive.

The other answer (i = i/1000 * 1000) rounds down when i is positive, but up when i is negative.

-13623 / 1000 * 1000 == -13000

There is also a version of Math.floorDiv for longs which will work for very large numbers where the Math.floor method might fail due to the precision of double.

There are also Math.floorMod methods to go with the floorDivs which might allow you to shorten it a bit:

int i = -13623;
i -= Math.floorMod(i, 1000);
//i => -14000