How to round a double value in Java.

Overview

In this post, we will learn how to round a double value in Java with the help of a small program.
First, let’s perform some calculation and try to print the double variable as shown below:

/**
 * 
 */
package questions;

import java.util.Scanner;

public class RoundDoubleExample {
  public static void main(String[] args) {
    double l;  // liters
    double g; // gallons 
    Scanner keyboard = new Scanner( System.in );
    System.out.print( "Enter liters := " ); 
    l = keyboard.nextDouble( ); 
    g = 0.264 * l;  
    System.out.print( l + " Liters = " );
    System.out.println( g + " gallons." );
    keyboard.close();
  } 
} 

Sample output of the program:

Enter liters := 3.785
3.785 Liters = 0.9992400000000001 gallons.

 

There are so many decimals printed in the output. In some cases, we may want to round the values to 2 or three decimal places. One reason could be the consistency in the output format. Lets us round the value to 3 decimal places.

Math.round()

We can round the variable to 3 decimal places by using Math.round() function.

(double)Math.round(gallons * 1000d) / 1000d

/**
 * 
 */
package questions;

import java.util.Scanner;

public class RoundDoubleExample {
  public static void main(String[] args) {
    double l;  // liters
    double g; // gallons 
    Scanner keyboard = new Scanner( System.in );
    System.out.print( "Enter liters := " ); 
    l = keyboard.nextDouble( ); 
    g = 0.264 * l;  
    System.out.print( l + " Liters = " );
    System.out.println( (double)Math.round(g * 1000d) / 1000d + " gallons." );
    keyboard.close();
  } 
} 

Enter liters := 3.785
3.785 Liters = 0.999 gallons.

 

 

Using DecimalFormat

DecimalFormat df = new DecimalFormat(“0.000”);

use df.format() to display the variable to round to 3 decimal places.

/**
 * 
 */
package questions;

import java.text.DecimalFormat;
import java.util.Scanner;

public class RoundDoubleExample {
  
  private static DecimalFormat df = new DecimalFormat("0.000");
  public static void main(String[] args) {
    double l;  
    double g;  
    Scanner keyboard = new Scanner( System.in );
    System.out.print( "Enter liters := " ); 
    l = keyboard.nextDouble( ); 
    g = 0.264 * l;  
    System.out.print( l + " Liters = " );
    System.out.println( df.format(g) + " gallons." );
    keyboard.close();
  } 
}