How to Format Numbers Using DecimalFormat in Java?

What is the best way to format numbers using DecimalFormat in Java?

DecimalFormat df = new DecimalFormat("#.##");
df.format(1234.5678); // Output: 1234.57

DecimalFormat in Java is a powerful class that provides the functionality to format decimal numbers according to specified patterns, enabling developers to display numbers in various formats such as currency, percentages, or standard decimal formats.

import java.text.DecimalFormat;

public class DecimalFormatExample {
    public static void main(String[] args) {
        DecimalFormat df = new DecimalFormat("###,###.00");
        System.out.println("Formatted Number: " + df.format(1234567.891)); // Output: Formatted Number: 1,234,567.89
    }
}

Causes

• Using incorrect pattern strings can yield unexpected results.
• Failing to import the necessary java.text package may lead to compilation errors.

Solutions

• Use the correct pattern strings in DecimalFormat to achieve desired output. For example, use "#.##" for two decimal places and do not forget to handle rounding appropriately.
• Always ensure to import the correct classes to avoid compilation errors.

Mistake: Using a pattern that does not match the expected number format resulting in incorrect output.

Solution: Double-check the pattern used in the DecimalFormat constructor; ensure it matches the desired format.

Mistake: Not rounding numbers properly before formatting.

Solution: Consider the effect of rounding and ensure the pattern chosen handles this as intended.