DecimalFormat

About

The DecimalFormat class in Java, part of the java.text package, is used for formatting and parsing decimal numbers in a locale-sensitive and customizable way. It allows precise control over the appearance of numeric values, such as rounding, grouping separators, and digit patterns.

• DecimalFormat is a concrete subclass of NumberFormat specifically designed for formatting decimal numbers.

• It provides pattern-based formatting to define how numbers appear (e.g., decimal places, grouping separators, currency symbols).

• The patterns can include digits, commas, dots, and special characters to create a specific format for numerical values.

Features

1. Pattern-Based Formatting: Allows defining custom patterns for numeric formats (e.g., "#.00" for two decimal places).

2. Locale-Sensitive: Adapts grouping separators and decimal symbols based on the locale.

3. Customizable Symbols: Supports setting custom symbols like grouping separators, decimal points, and prefixes.

4. Rounding Behavior: Automatically rounds numbers based on the defined pattern.

5. Parsing Capability: Can parse formatted strings back into numerical values.

6. Thread-Safety: Not thread-safe but can be synchronized or used with thread-local storage.

Declaration

To use DecimalFormat, import it from the java.text package:

import java.text.DecimalFormat;

Common Methods

1. Formatting:

   • String format(double number): Formats a double into a String based on the pattern.

   • String format(long number): Formats a long into a String.

2. Parsing:

   • Number parse(String source): Parses a formatted String into a Number.

3. Customization:

   • setMaximumFractionDigits(int newValue): Sets the maximum number of digits allowed after the decimal point.

   • setMinimumFractionDigits(int newValue): Sets the minimum number of digits required after the decimal point.

   • setGroupingUsed(boolean newValue): Enables or disables the use of grouping separators (commas, spaces, etc.).

4. Symbols Customization:

   • setDecimalFormatSymbols(DecimalFormatSymbols newSymbols): Sets custom symbols like decimal points or grouping separators.

Usage

Basic Number Formatting

import java.text.DecimalFormat;

public class DecimalFormatExample {
    public static void main(String[] args) {
        DecimalFormat df = new DecimalFormat("#.00");

        double value = 12345.6789;
        System.out.println("Formatted Value: " + df.format(value));
    }
}

Output:

Formatted Value: 12345.68

Customizing Patterns

import java.text.DecimalFormat;

public class CustomPatternExample {
    public static void main(String[] args) {
        DecimalFormat df = new DecimalFormat("#,###.##");

        double value = 1234567.89;
        System.out.println("Custom Pattern: " + df.format(value));
    }
}

Output:

Custom Pattern: 1,234,567.89

Parsing Numbers

import java.text.DecimalFormat;
import java.text.ParseException;

public class ParsingExample {
    public static void main(String[] args) {
        DecimalFormat df = new DecimalFormat("#,###.##");

        String formattedValue = "1,234,567.89";
        try {
            Number number = df.parse(formattedValue);
            System.out.println("Parsed Value: " + number);
        } catch (ParseException e) {
            System.out.println("Error parsing the number.");
        }
    }
}

Output:

Parsed Value: 1234567.89

Custom Symbols

import java.text.DecimalFormat;
import java.text.DecimalFormatSymbols;

public class CustomSymbolsExample {
    public static void main(String[] args) {
        DecimalFormatSymbols symbols = new DecimalFormatSymbols();
        symbols.setDecimalSeparator(',');
        symbols.setGroupingSeparator('.');

        DecimalFormat df = new DecimalFormat("#,###.##", symbols);

        double value = 1234567.89;
        System.out.println("Custom Symbols: " + df.format(value));
    }
}

Output:

Custom Symbols: 1.234.567,89

Real-World Example

import java.text.DecimalFormat;

public class RealWorldExample {
    public static void main(String[] args) {
        DecimalFormat usFormat = new DecimalFormat("$###,###.00");

        double payment = 12324.134;

        // US Formatting
        System.out.println("US: " + usFormat.format(payment));

        // Custom Locale Formatting
        DecimalFormat indiaFormat = new DecimalFormat("Rs.###,###.00");
        System.out.println("India: " + indiaFormat.format(payment));
    }
}

Output:

US: $12,324.13
India: Rs.12,324.13