In Java, the fastest and most convenient way to round a decimal number is using the BigDecimal class. Let’s say, we want to round some numbers like this:

• 7.2314 is rounded to 7.23 (two digits after decimal point).
• 8.3868 is rounded to 8.4 (one digit after decimal point).

Here’s a very simple utility class that rounds an arbitrary decimal number with the number of digits after decimal point can be specified:

package net.codejava.core;

import java.math.BigDecimal;

/**
 * This utility class rounds a decimal number.
 * @author www.codejava.net
 *
 */
public class DecimalUtils {

	public static double round(double value, int numberOfDigitsAfterDecimalPoint) {
		BigDecimal bigDecimal = new BigDecimal(value);
		bigDecimal = bigDecimal.setScale(numberOfDigitsAfterDecimalPoint, 
				BigDecimal.ROUND_HALF_UP);
		return bigDecimal.doubleValue();
	}
}

The important point in this utility class is the setScale() method of the BigDecimal class. It accepts two parameters:

• The first parameter specifies number of digits after decimal point which the rounding will be carried out toward.
• The second parameter specifies round mode. Here, we use the ROUND_HALF_UP which rounds up the number toward the “nearest neighbor”. The BigDecimal class defines all possible round modes, including ROUND_HALF_DOWN, ROUND_HALF_EVEN, etc.

And the following is a test program:

package net.codejava.core;

/**
 * Test rounding decimal numbers.
 * @author www.codejava.net
 *
 */
public class DecimalUtilsTest {

	public static void main(String[] args) {
		double number = 91.2139;
		double roundedNumber = DecimalUtils.round(number, 2);
		System.out.println(number + " is rounded to: " + roundedNumber);
		
		roundedNumber = DecimalUtils.round(number, 3);
		System.out.println(number + " is rounded to: " + roundedNumber);
		
		number = 80.37723;
		roundedNumber = DecimalUtils.round(number, 2);
		System.out.println(number + " is rounded to: " + roundedNumber);
		
		roundedNumber = DecimalUtils.round(number, 3);
		System.out.println(number + " is rounded to: " + roundedNumber);
	}

}

Output:

91.2139 is rounded to: 91.21

91.2139 is rounded to: 91.214

80.37723 is rounded to: 80.38

80.37723 is rounded to: 80.377

 

References:

• BigDecimal class Javadoc.

 

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