Always Round UP a Double

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.

In simple words,

• Math.ceil will always round UP or as said above, in excess.
• Math.round will round up or down depending on the decimals.
  • If the decimal is equal or higher than 5, then it's rounded up.
    • decimal => 5. (1,5 = 2)
  • If the decimal is less than 5, then it's rounded down.
    • decimal < 5. (1,45 = 1)

Examples of Math.ceil and Math.round:

The code Below would return:
Cost, without Ceil 2.2 and with Ceil 3 (int), 3.0 (double). If we round it: 2

    int m2 = 2200;
    double rate = 1000.0;

    int costceil = (int)Math.ceil(m2/rate);
    double costdouble = m2/rate;
    double costdoubleceil = Math.ceil(m2/rate);
    int costrounded = (int)Math.round(m2/rate);
    System.out.println("Cost, without Ceil "+costdouble+" and with Ceil "+
            costceil+"(int), "+costdoubleceil+"(double). If we round it: "+costrounded);

If we change the value of m2 to for example 2499, the result would be: Cost, without Ceil 2.499 and with Ceil 3 (int), 3.0 (double). If we round it: 2
If we change the value of m2 to for example 2550, the result would be:
Cost, without Ceil 2.55 and with Ceil 3 (int), 3.0 (double). If we round it: 3

Hope it helps. (Information extracted from previous answers, i just wanted to make it clearer).

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.