Java Format Precision

In this chapter you will learn:

1. How to use precision modifier
2. Syntax for Precision Format
3. Example - Precision Format
4. How to format decimal value in precision
5. How to control the number of significant digits for %g
6. How to control string length with precision specifier
7. Example - Specifying a Minimum Field Width

Description

A precision specifier can be applied to the %f, %e, %g, and %s format specifiers and follows the minimum field-width specifier if there is one. A precision specifier consists of a period followed by an integer.

The precision specifier added to floating-point data using the %f or %e specifiers, the precision specifier determines the number of decimal places displayed.

Syntax

Example

Precision Format

import java.util.Formatter;
//from   w w w  .  j a  v a  2  s .  co m
public class Main {
  public static void main(String args[]) {
    Formatter fmt = new Formatter();
    // Format to 2 decimal places in a 16 character field.
    fmt = new Formatter();
    fmt.format("%16.2e", 123.1234567);
    System.out.println(fmt);

  }
}

The output:

Example 2

For example, %10.4f displays a number at least ten characters wide with four decimal places.

// Demonstrate the precision modifier. 
import java.util.Formatter;
//from   www .  j a v a 2  s  .co m
public class Main {
  public static void main(String args[]) {
    Formatter fmt = new Formatter();
    // Format 4 decimal places.
    fmt.format("%.4f", 123.1234567);
    System.out.println(fmt);
  }
}

The output:

Example 3

The %g format specifier causes Formatter to use either %f or %e, whichever is shorter.

When using %g, the precision determines the number of significant digits. The default precision is 6.

import java.util.Formatter;
/*from   www .j  av a 2 s . c  om*/
public class Main {
  public static void main(String args[]) {
    Formatter fmt = new Formatter();
    fmt.format("%g\n", 123.1234567);
    // Format 4 decimal places.
    fmt.format("%.4g", 123.1234567);
    System.out.println(fmt);
  }
}

The output:

Example 4

When the precision specifier is applied to strings, the precision specifier specifies the maximum field length. For example, %5.7s displays a string at least five and not exceeding seven characters long. If the string is longer than the maximum field width, the end characters will be truncated.

import java.util.Formatter;
/*from  w  w  w.jav a2  s.co m*/
public class Main {
  public static void main(String args[]) {
    Formatter fmt = new Formatter();
    // Display at most 15 characters in a string.
    fmt = new Formatter();
    fmt.format("%.15s", "12345678901234567890");
    System.out.println(fmt);

  }
}

Example 5

An integer between the % sign and the format conversion code acts as a minimum field width specifier.

The default padding is done with spaces.

If you want to pad with 0's, place a 0 before the field width specifier.

For example, %05d will pad a number of less than five digits with 0's.

import java.util.Formatter;
//  w  w w. jav a  2 s.com
public class Main {
  public static void main(String args[]) {
    Formatter fmt = new Formatter();

    fmt.format("%05d", 88);
    System.out.println(fmt);
  }
}

The code above generates the following result.

Next chapter...

What you will learn in the next chapter:

1. What are format flags
2. Flag List

Java Format Precision