Math.ceil

Integers have no fractional parts. With the floor and ceiling functions we compute integers. A floor is the lower integer, and a ceiling is the higher one.

To compute a ceiling, we invoke Math.ceil. This method receives, and returns, a double value. If passed a number with no fractional part, that number is returned unchanged.

First example

With this method, a number is always increased if it has a fractional part. It does not matter how close to the lower number the number is. It is increased by ceil().

import java.lang.Math;

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

        // Compute ceilings of these values.
        double value = Math.ceil(1.1);
        double value2 = Math.ceil(-0.9);

        System.out.println(value);
        System.out.println(value2);
    }
}
2.0
-0.0

Ceiling, floor study

This program studies the result of floor and ceil. For numbers with no fractional part (like 1.0 or 2.0) we find that the ceiling and floor are equal.

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

        // Analyze these numbers.
        double[] values = { 1.0, 1.1, 1.5, 1.9, 2.0 };

        for (double value : values) {

            // Compute the floor and the ceil for the number.
            double floor = Math.floor(value);
            double ceil = Math.ceil(value);

            // See if the floor equals the ceil.
            boolean equal = floor == ceil;

            // Print the values.
            System.out.println(value + ", Floor = " + floor +
                    ", Ceil = " + ceil +
                    ", Equal = " + equal);
        }
    }
}
1.0, Floor = 1.0, Ceil = 1.0, Equal = true
1.1, Floor = 1.0, Ceil = 2.0, Equal = false
1.5, Floor = 1.0, Ceil = 2.0, Equal = false
1.9, Floor = 1.0, Ceil = 2.0, Equal = false
2.0, Floor = 2.0, Ceil = 2.0, Equal = true

With the Math class, we gain many powerful and well-tested methods. Math.ceil is similar to Math.floor. And programs that use one often use the other.