How to Use DecimalFormat in Java to Add Leading Zeros

How can I pad numbers with leading zeros using DecimalFormat in Java?

DecimalFormat df = new DecimalFormat("00"); // Pads the number with leading zeros
String paddedNumber = df.format(5); // Result: "05"

In Java, the DecimalFormat class is a powerful tool for formatting decimal numbers. It allows you to specify patterns for formatting, including adding leading zeros to numbers. This feature is particularly useful when you want numbers to conform to a specific width, such as when displaying IDs, order numbers, or formatting time.

import java.text.DecimalFormat;

public class Main {
    public static void main(String[] args) {
        DecimalFormat df = new DecimalFormat("00"); // Pads single digit numbers
        String paddedNumber1 = df.format(7); // Output: 07
        String paddedNumber2 = df.format(12); // Output: 12
        System.out.println(paddedNumber1);
        System.out.println(paddedNumber2);
    }
}

Causes

• Without proper formatting, numbers may not display as intended (e.g., '5' instead of '05').
• Leading zeros are often necessary for alignment in display or data processing.

Solutions

• Utilize the DecimalFormat class to define a pattern that includes leading zeros. For instance, "00" will ensure that any number less than two digits will be padded with a zero.
• Create a DecimalFormat instance with the desired pattern, and then use the format method for your number.

Mistake: Using a pattern without leading zeros results in no padding.

Solution: Ensure to specify a pattern like "00", "000", etc., based on the required width.

Mistake: Not importing the DecimalFormat class.

Solution: Add the line 'import java.text.DecimalFormat;' at the top of your Java file.