How to Add Leading Zeroes to Numbers in Java?

Add Leading Zeroes to Number in Java

This article provides a solution to adding leading zeroes to a number in Java.

Custom Method

A custom method called intToString is created to address this requirement. It takes the original number (num) and the desired number of digits. It calculates the number of zeroes needed to equal the desired number of digits based on the number of digits in num. Then, it appends the zeroes and the original number to a StringBuffer before converting it to a string.

static String intToString(int num, int digits) {
    StringBuffer s = new StringBuffer(digits);
    int zeroes = digits - (int) (Math.log(num) / Math.log(10)) - 1; 
    for (int i = 0; i < zeroes; i++) {
        s.append(0);
    }
    return s.append(num).toString();
}

String.format() Method (Java 5 )

Java 5 introduced the String.format() method, which offers a more elegant solution for this task. It allows you to specify the padding and width requirements directly in the format string.

String formatted = String.format("%03d", num);

In this example:

• d specifies that the number should be formatted as a decimal integer with a minimum width of 3 characters.
• Leading zeroes will be used to pad the number to the specified width.

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