Java - Number Custom Format with DecimalFormat

Introduction

DecimalFormat allows you to supply your own format pattern.

Once you create an object of the DecimalFormat class, you can change the format pattern using its applyPattern() method.

You can specify different patterns for positive and negative numbers.

The two patterns are separated by a semicolon.

DecimalFormat class uses round-to-even rounding mode while formatting numbers.

You can parse a string to a number using the parse() method.

parse() method returns an object of the java.lang.Number class.

You can use xxxValue() methods to get the primitive value, where xxx can be byte, double, float, int, long, and short.

The following code illustrates the use of the DecimalFormat class.

Demo

import java.text.DecimalFormat;
import java.text.ParsePosition;

public class Main {
  private static DecimalFormat formatter = new DecimalFormat();

  public static void main(String[] args) {
    formatNumber("##.##", 12.745);
    formatNumber("##.##", 12.746);
    formatNumber("0000.0000", 12.735);
    formatNumber("#.##", -12.735);

    // Positive and negative number format
    formatNumber("#.##;(#.##)", -12.735);

    // Parse a string to decimal number
    String str = "XY4,123.983";
    String pattern = "#,###.###";
    formatter.applyPattern(pattern);/*from  www.j a va2  s .  co m*/

    // Create a ParsePosition object to specify the first digit of
    // number in the string. It is 4 in "XY4,123.983"
    // with the index 2.
    ParsePosition pp = new ParsePosition(2);

    Number numberObject = formatter.parse(str, pp);

    double value = numberObject.doubleValue();
    System.out.println("Parsed Value is " + value);
  }

  public static void formatNumber(String pattern, double value) {
    // Apply the pattern
    formatter.applyPattern(pattern);

    // Format the number
    String formattedNumber = formatter.format(value);

    System.out.println("Number:" + value + ", Pattern:" + pattern
        + ", Formatted Number:" + formattedNumber);
  }
}

Result