How to round up integer division and have int result in Java?

Question

I just wrote a tiny method to count the number of pages for cell phone SMS. I didn't have the option to round up using Math.ceil, and honestly it seems to be very ugly.

Here is my code:

public class Main {

/**
 * @param args the command line arguments
 */
public static void main(String[] args) {
   String message = "today we stumbled upon a huge performance leak while optimizing a raycasting algorithm. Much to our surprise, the Math.floor() method took almost half of the calculation time: 3 floor operations took the same amount of time as one trilinear interpolation. Since we could not belive that the floor-method could produce such a enourmous overhead, we wrote a small test program that reproduce";

   System.out.printf("COunt is %d ",(int)messagePageCount(message));



}

public static double messagePageCount(String message){
    if(message.trim().isEmpty() || message.trim().length() == 0){
        return 0;
    } else{
        if(message.length() <= 160){
            return 1;
        } else {
            return Math.ceil((double)message.length()/153);
        }
    }
}

I don't really like this piece of code and I'm looking for a more elegant way of doing this. With this, I'm expecting 3 and not 3.0000000. Any ideas?

Answer 1

Ceiling

Normal integer division rounds to zero, truncating any fraction.

Instead, what you want is to round toward positive infinity, known as the ceiling.

Math.ceilDiv

In Java 18+, use Math.ceilDiv. Pass your two int values, dividend and divisor. Returns an int.

int x = 15 / 8 ;                 // 1
int y = Math.ceilDiv ( 15 , 8 )  // 2

Math.ceil

In earlier Java, use Math.ceil(), casting the result to int.

• This is still faster than to avoid doubles by using abs().
• The result is correct when working with negatives, because -0.999 will be rounded UP to 0

Syntax:

(int) Math.ceil( (double) dividend / divisor );

int x = 15 / 8 ;                                  // 1
int y = ( int ) Math.ceil ( ( double ) 15 / 8 );  // 2