How to Truncate the Double Value to Given Decimal Places in Java?

In simplest terms, truncation means to chop off the decimal portion of a number. A method of approximating a decimal number by dropping all decimal places past a certain point without rounding.

Given a double value and a decimal place truncate the value to the given decimal point.

Example: 

Input: val = 3.142857142857143
Decimal point = 3
Output =  3.142

Upto 3 decimal places

 Approach 1: Using Mathematically :

• Shift the decimal of the given value to the given decimal point by multiplying 10^n
• Take the floor of the number and divide the number by 10^n
• The final value is the truncated value

Java

// Java program to truncate the double value to
// a particular decimal point

import java.io.*;

class GFG {

    static void change(double value, int decimalpoint)
    {

        // Using the pow() method
        value = value * Math.pow(10, decimalpoint);
        value = Math.floor(value);
        value = value / Math.pow(10, decimalpoint);

        System.out.println(value);

        return;
    }

      // Main Method
    public static void main(String[] args)
    {

        double firstvalue = 1212.12131131;
        int decimalpoint = 4;

        change(firstvalue, decimalpoint);

        double secondvalue = 3.142857142857143;
        int decimalpoint2 = 3;

        change(secondvalue, decimalpoint2);
    }
}

Output

1212.1213
3.142

Approach 2: Using String matching approach

• Convert the number into String
• Start the counter variable when “.” found in the String
• Increment the counter till decimal point
• Store the new String and parse it in double format

Java

// Java program to truncate the double
// value using string matching

import java.io.*;

class GFG {
    public static void main(String[] args)
    {
        double firstvalue = 1212.12131131;

        // decimal point
        int decimalpoint = 6;

        // convert the double value in string
        String temp_value = "" + firstvalue;
        String string_value = "";

        int counter = -1;

        for (int i = 0; i < temp_value.length(); ++i) {

            // checking the condition
            if (counter > decimalpoint) {
                break;
            }
            else

                if (temp_value.charAt(i) == '.') {
                counter = 1;
            }
            else if (counter >= 1) {

                ++counter;
            }

            // converting the number into string
            string_value += temp_value.charAt(i);
        }

        // parse the string
        double new_value = Double.parseDouble(string_value);

        System.out.println(new_value);
    }
}

Output

1212.121311