Java Program to Round a Number to n Decimal Places

10 May, 2022
Floating-point numbers are decimal values, which can be rounded to n number of decimal places. There are 3 different ways to Round a Number to n Decimal Places in Java as follows: 
Using format MethodUsing DecimalFormat ClassMultiply and Divide the number by 10n (n decimal places)
Using format Method
Using DecimalFormat Class
Multiply and Divide the number by 10n (n decimal places)
Example:
Input: number = 1.41421356237, round = 3 
Output:1.414
Input: number = 0.70710678118, round = 2 
Output:0.71
The decimal number can be rounded by the inbuilt format() method supported by Java. 
Syntax: 
System.out.format("%.df", number);
Parameters: The first parameter accepts d digits to round off the number, the second argument accepts a number that is to be rounded.
Example:
Java
// Java Program to Round a Number to n Decimal Places// using format() Method // Importing required classesimport java.io.*; // Main classclass GFG {     // Main driver method    public static void main(String[] args)    {        // Declaring and initializing a double number        double number = 3.141341435;         // Rounding number to 2 decimal places        // using format method        System.out.format("%.2f", number);    }}
3.14
DecimalFormat is a child class of the NumberFormat which is used to perform formatting of decimal numbers in java. We create an object of this class and pass in as arguments the format specified in form of #, with the number of # after decimal point indicating the number of digits we wish to output. By default, the number is rounded off to the ceiling value itself. The object of the DecimalFormat class invokes a method format() which takes as argument the number to be formatted.
Example 1:
Java
// Java Program to Round a Number to n Decimal Places// Using DecimalFormat Class // Importing required classesimport java.text.DecimalFormat; // Main classpublic class GFG {     // Main driver method    public static void main(String[] args)    {        // Declaring and initializing a double number        double number = 145.34567;         // Creating an object of DecimalFormat class        DecimalFormat df_obj = new DecimalFormat("#.###");         // format() method is used to        // print the desired number        System.out.println(df_obj.format(number));    }}
145.346
Note: In case we wish to round off the number to the floor, we invoke the Java in-built class RoundingMode. It has the following values for attributes as follows:
FLOOR – for next nearest floor value
CEILING – for next nearest ceiling value
Also do remember, this method can be invoked on the DecimalFormat class supported in-built method setRoundingMode(), which takes as an argument either RoundingMode.FLOOR or CEILING, and accordingly gives us the result.
Example 2:
Java
// Java Program to Round a Number to N Decimal Places// Using DecimalFormat Class // Importing required classesimport java.math.RoundingMode;import java.text.DecimalFormat; // Main classpublic class GFG {     // Main driver method    public static void main(String[] args)    {         // Declaring and initializing double        double number = 9.97869896;         // Creating an object of DecimalFormat class        DecimalFormat df_obj = new DecimalFormat("#.####");         // Rounding number to the next lowest value        // using setRoundingMode()        df_obj.setRoundingMode(RoundingMode.FLOOR);         // Printing the number in desired format        // using format() method        System.out.println(df_obj.format(number));    }}
9.9786
 In this approach, we first Multiply the number by 10n using the pow() function of the Math class. Then the number is rounded to the nearest integer. At last, we divide the number by 10n. By doing this, we get the decimal number up to n decimal places.
Syntax:
number = Math.round(number*Math.pow(10,n))/Math.pow(10,n);
Example:
Java
// Java Program to Round a Number to n Decimal Places// Via Multiply and Divide the number with 10^n // Importing required classesimport java.io.*; // Main classclass GFG {     // Main driver method    public static void main(String[] args)    {         // Declaring and initializing double number        double number = 12.983665;         // Getting the number of decimal places required        int n = 3;         // Rounding off the number        // using pow() and round() method of Math class        number = Math.round(number * Math.pow(10, n))                 / Math.pow(10, n);         // Printing the rounded number        System.out.println(number);    }}
Output
12.984
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