Java Program to Round a Number to n Decimal Places
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 Method
- Using DecimalFormat Class
- Multiply and Divide the number by 10n (n decimal places)
Input: number = 1.41421356237, round = 3 Output:1.414
Input: number = 0.70710678118, round = 2 Output:0.71
Method 1: Using format Method
The decimal number can be rounded by the inbuilt format() method supported by Java.
Parameters: The first parameter accepts d digits to round off the number, the second argument accepts a number that is to be rounded.
Method 2: Using DecimalFormat Class
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.
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.
Method 3: Multiply and Divide the number with 10n (n decimal places)
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.
number = Math.round(number*Math.pow(10,n))/Math.pow(10,n);
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