Math.floor

This Java function maps a number to the nearest lowest integer. For example 4.9 is mapped to 4. It works on negative numbers too: -3.1 maps to -4.

With related methods, floorDiv and floorMod we compute a division expression and then take the floor of that result. Div is division, and mod is modulo division.

Floor example

The floor is always beneath us. Likewise the Math.floor method always returns a lower integer. For negative numbers, floor() still lowers.

import java.lang.Math;

public class Program {
    public static void main(String[] args) {

        // These are all reduced, even the negative number.
        double floor1 = Math.floor(1.9);
        double floor2 = Math.floor(1.1);
        double floor3 = Math.floor(-1.3);

        System.out.println(floor1);
        System.out.println(floor2);
        System.out.println(floor3);
    }
}
1.0
1.0
-2.0

FloorDiv

9 divided by 2 is 4.5, but with floorDiv we take the floor of that result. This returns 4. So floorDiv combines division with Math.floor.

public class Program {
    public static void main(String[] args) {

        // Use Math.floorDiv to compute the floor of a division.
        // ... The first argument is the number being divided.
        // ... The second argument is the divisor.
        int result = Math.floorDiv(9, 2);
        System.out.println(result);

        // This is the same division with no floor.
        double result2 = (double) 9 / 2;
        System.out.println(result2);
    }
}
4
4.5

FloorMod

This method is the same as floorDiv except it uses modulo division. In most cases it is the same as a regular modulo division.

public class Program {
    public static void main(String[] args) {

        // The remainder of 10 modulo 6 is 4.
        int result = Math.floorMod(10, 6);
        int result2 = 10 % 6;
        System.out.println(result);
        System.out.println(result2);

        // Use negative numbers mixed with positive numbers.
        // ... These are different with floorMod.
        int result3 = Math.floorMod(10, -6);
        int result4 = 10 % -6;
        System.out.println(result3);
        System.out.println(result4);
    }
}
4
4
-2
4

A review

The floor functions in Java are present alongside ceiling functions. We map numbers to the nearest lower (for floor) or higher (for ceiling) integers.