Always Round UP a Double

Question

How could I always round up a double to an int, and never round it down. I know of Math.round(double), but I want it to always round u

Answer 1

private int roundUP(double d){
    double dAbs = Math.abs(d);
    int i = (int) dAbs;
    double result = dAbs - (double) i;
    if(result==0.0){ 
        return (int) d;
    }else{
        return (int) d<0 ? -(i+1) : i+1;          
    }
}

Good job ! ;)

Answer 2

Math.ceil() will give you the closest lowest value if you want it to be rounded to largest closest values you should use Math.floor()

Answer 3

Short example without using Math.ceil().

public double roundUp(double d){
    return d > (int)d ? (int)d + 1 : d;
}

Exaplanation: Compare operand to rounded down operand using typecast, if greater return rounded down argument + 1 (means round up) else unchanged operand.

Example in Pseudocode

double x = 3.01
int roundDown = (int)x   // roundDown = 3
if(x > roundDown)        // 3.01 > 3
    return roundDown + 1 // return 3.0 + 1.0 = 4.0
else
    return x             // x equals roundDown

Anyway you should use Math.ceil(). This is only meant to be a simple example of how you could do it by yourself.

Answer 4

tl;dr

BigDecimal( "3.2" ).setScale( 0 , RoundingMode.CEILING )

4

BigDecimal

If you want accuracy rather than performance, avoid floating point technology. That means avoiding float, Float, double, Double. For accuracy, use BigDecimal class.

On a BigDecimal, set the scale, the number of digits to the right of the decimal place. If you want no decimal fraction, set scale to zero. And specify a rounding mode. To always round an fraction upwards, use RoundingMode.CEILING, documented as:

Rounding mode to round towards positive infinity. If the result is positive, behaves as for RoundingMode.UP; if negative, behaves as for RoundingMode.DOWN. Note that this rounding mode never decreases the calculated value. So for example, 1.1 becomes 2, and your 3.2 becomes 4.

BigDecimal bd = new BigDecimal( "3.2" ) ;
BigDecimal bdRounded = bd.setScale( 0 , RoundingMode.CEILING ) ;
String output = bdRounded.toString() ; 
System.out.println( "bdRounded.toString(): " + bdRounded ) ;  // 4

4

See this code run live at IdeOne.com.

Answer 5

You can use Math.ceil() method.

See JavaDoc link: https://docs.oracle.com/javase/10/docs/api/java/lang/Math.html#ceil(double)

From the docs:

ceil

public static double ceil(double a)

Returns the smallest (closest to negative infinity) double value that is greater than or equal to the argument and is equal to a mathematical integer. Special cases:

• If the argument value is already equal to a mathematical integer, then the result is the same as the argument.
• If the argument is NaN or an infinity or positive zero or negative zero, then the result is the same as the argument.
• If the argument value is less than zero but greater than -1.0, then the result is negative zero.

Note that the value of Math.ceil(x) is exactly the value of -Math.floor(-x).

Parameters:

• a - a value.

Returns:

The smallest (closest to negative infinity) floating-point value that is greater than or equal to the argument and is equal to a mathematical integer.

Answer 6

My method is relatively simple, hope it works for you.

In my case I have a row of objects that can only hold 3 items and I must adjust the number of rows I have to accommodate the items.

So I have some Double numberOfRows, I then use numberOfRows.intValue() to get an int value for numberOfRows.

if the int value I get is less than numberOfRows, I add 1 to numberOfRows to round it up, else the value I get from numberOfRows.intValue() is the answer I want.

I wrote this simple for loop to test it out:

    for(int numberOfItems = 0; numberOfItems < 16; numberOfItems++) {
        Double numberOfRows = numberOfItems / 3.0;

        System.out.println("Number of rows are: " + numberOfRows);
        System.out.println("Number of items are: " + numberOfItems);
        if(numberOfRows.intValue() < numberOfRows) {
            System.out.println("int number of rows are: " + (numberOfRows.intValue() + 1));
        }
        else {
            System.out.println("int value of rows are: " + numberOfRows.intValue());
        }
        System.out.println();
        System.out.println();
    }