How to Set Precision For Double Values in Java?

Significant digits are referred to all digits inclusive of left and right to decimal place keeping a note adding 0 to left of any number is not countable as significant digits whereas precise digits referred to digits that are only lying on the right side or in short after the decimal place in mathematics. In Java, there are numbers more than 16 numbers only to the precision but can go more. Here we are given a double value, the task is to set its precision value to specific decimal places. It is illustrated below illustrations as follows:

Illustrations:

Input  : val = 1 
Output : 1.0000
Upto 4 decimal places

Input  : 12.5
Output : 12.500000
Upto 6 decimal places

Different Methods to Set Precision in Double Values

1. Using format() Method of String class
2. Using round() method of Math class

Method 1: Using the format() Method of the String class

We can use format() method of String class to format the decimal number to some specific format.

Syntax:

String.format("%.Df", decimalValue);
// Where D is the number required number of Decimal places

Example-1:

Java

// Java Program to Illustrate format() Method
// of String class

// Importing required classes
import java.io.*;
import java.lang.*;

// Class
class GFG {

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

     // Declaring and initializing
     // double value
    double a = 0.9;

    // Setting the precision
    // to 20 places
    System.out.println(
      String.format("%.20f", a));

    double b = 1;

    // Setting the precision
    // to 5 places
    System.out.println(
      String.format("%.5f", b));
  }
}

Output

0.90000000000000000000
1.00000

From the above output, it is clear that precision of 20 digits is been carried out for the first entry whereas precision to 5 digits is carried out on input double value. 

Example-2:

Java

// Demonstrating the precision modifier

import java.util.*;

class GFG {
    public static void main (String[] args) {
      Formatter fm=new Formatter();

      // Format 4 decimal places
      fm.format("%.4f", 123.1234567);
      System.out.println(fm);
      fm.close();

      //Format 2 decimal places in a 16 charcater field
      fm=new Formatter();
      fm.format("%16.2e",123.1234567);
      System.out.println("GFG!");
      fm.close();

      //Display atmost 15 characters in a string
      fm=new Formatter();
      fm.format("%.15s", "Learning with Gfg is easy quick");
      System.out.println(fm);
      fm.close();
    }
}

Output

123.1235
GFG!
Learning with G

Method 2: Using round() method of Math Class

Example:

Java

// Java Program to Illustrate Precision Setting In Double
// Using round() Method of Math Class

// Importing required classes
import java.util.*;

// Class
class GFG {

    // Main driver method
    public static void main(String[] args)
    {
        // Declaring and initializing double variable
        double num = 3.141414141414;

        // Rounding off above double number
        // to 7 precision
        double ans
            = Math.round(num * 10000000) / 10000000.0;

        // Printing the above precised value
        // of double value
        System.out.println(ans);
    }
}

Output

3.1414141

The above double number is precise to 7 digits which can easily be seen from the output generated.