How to Use DecimalFormat Patterns in Java for Number Formatting

What are DecimalFormat patterns and how can I use them in Java?

DecimalFormat df = new DecimalFormat("#.##");
df.format(12.34567); // Returns "12.35"

DecimalFormat is a class in Java used for formatting decimal numbers. It allows developers to specify how a number should be displayed, making it easier to manage output standards in applications.

import java.text.DecimalFormat;

public class NumberFormatting {
    public static void main(String[] args) {
        DecimalFormat df = new DecimalFormat("#0.00");
        String formattedNumber = df.format(12345.6789);
        System.out.println(formattedNumber); // Outputs "12345.68"
    }
}

Causes

• Need to format numbers in a user-friendly manner.
• Requirement for currency formatting or percentage representation.
• Displaying a specific number of decimal places.

Solutions

• Use DecimalFormat class with custom patterns to tailor number formatting.
• Utilize pre-defined formats like '0.00' for two decimal places or '#,###' for thousand separators.
• Experiment with patterns to achieve the desired output format.

Mistake: Incorrect pattern resulting in unexpected formatting.

Solution: Ensure the pattern string matches the intended output. For example, use '0' for mandatory digits and '#' for optional.

Mistake: Not considering rounding behavior.

Solution: Remember that DecimalFormat rounds according to its rules. Use Math.round() if precise rounding is needed before formatting.