Truncate Double in Java

  1. Use DecimalFormat to Truncate Double in Java
  2. Use BigDecimal to Truncate Double in Java
  3. Use Apache Common Library to Truncate Decimal in Java
  4. Use java.lang.Math to Truncate Decimal in Java

In this article, we will look at how to truncate or round off a number to n decimal points in Java. Java provides two primitive types to store decimal values which are double and float. It is recommended to use the BigDecimal class for precise values or rounding off.

Use DecimalFormat to Truncate Double in Java

DecimalFormat is a subclass of NumberFormat that can format decimal numbers using the formatting pattern provided. Here in the code below, we created an object of DecimalFormat passing a suitable formatting pattern. We can call the format() method on the decimatFormat object and pass our double variable d as a parameter.

The format() method returns a string that is truncated, as shown in the output.

import java.text.DecimalFormat;
public class DecimalFormatting {
    public static void main(String args[]){
        double d = 9.4568982982989;
        String pattern = "#.###";
        DecimalFormat decimalFormat =  new DecimalFormat(pattern);
        String formattedDouble = decimalFormat.format(d);
        System.out.println("Formatted double d = "+formattedDouble);
    }
}

Output:

Formatted double d = 9.457

Use BigDecimal to Truncate Double in Java

In Java, BigDecimal are immutable, arbitrary-precision signed decimal numbers. It provides control over scale and precision. We create a BigDecimal object passing the double converted as a string, preventing issues with representing approximate values.

We then call the setScale(int newScale, RoundingMode roundingMode) method on this BigDecimal object bd, which takes two arguments: the scale of BigDecimal to be returned and the other is the rounding mode to apply. The mode RoundingMode.FLOOR rounds towards negative infinity.

public class DecimalFormatting {
    public static void main(String args[]){
        double d = 9.4568982982989;
        BigDecimal bd = new BigDecimal(String.valueOf(d));
        BigDecimal rounded = bd.setScale(2,RoundingMode.FLOOR);
        System.out.println("BigDecimal rounded off : "+rounded);
    }
}

Output:

BigDecimal rounded off : 9.45

Use Apache Common Library to Truncate Decimal in Java

We can achieve the same by this library whose maven dependency is given below.

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-math3</artifactId>
    <version>3.5</version>
</dependency>

We can use the Precision.round() method from this library to format decimal. This method takes two arguments, one the decimal variable to be formatted and scale. We need 4 digits after the decimal point; hence that’s the scale we need. The output shows digits in the decimal are truncated.

import org.apache.commons.math3.util.Precision;
public class DecimalFormatting {
    public static void main(String args[]){
        double d = 9.4568982982989;
        double doubleP = Precision.round(d,4);
        System.out.println("Precision rounded off : "+doubleP);
    }
}

Output:

Precision rounded off : 9.4569

Use java.lang.Math to Truncate Decimal in Java

This is another way to round off decimal numbers in Java. The method Math.pow() to control n number of decimal places by multiplying and dividing by 10^n. We create a double variable scale using this method which takes two arguments, base 10 and power 3.

Math.round() in Java is used to round a number to its closest integer. This is done by adding 12 to the number, talking the floor of the result, and casting the result to an integer data type. This method is not recommended as it sometimes truncates the value incorrectly.

public class DecimalFormatting {
    public static void main(String args[]){
         double d = 9.4568982982989;
         double scale = Math.pow(10, 3);
         double doubleM1 = Math.round(d*scale)/scale;
         System.out.println("Math1 Rounded off: "+doubleM1);
    }
}

Output:

Math Rounded off: 9.45
Math1 Rounded off: 9.457
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