Left padding a String with Zeros

To left pad a String with zeros in Java, you can use the String.format() method and the %0Nd format specifier, where N is the total length of the padded string.

For example, to left pad a string with 5 zeros, you can use the following code:

String s = "123";
String padded = String.format("%05d", Integer.parseInt(s));  // padded is "00123"

The %05d format specifier tells the String.format() method to format the integer value as a decimal number with a total length of 5, and to pad the number with zeros on the left if necessary.

You can also use the DecimalFormat class to left pad a string with zeros. For example:

String s = "123";
DecimalFormat df = new DecimalFormat("00000");
String padded = df.format(Integer.parseInt(s));  // padded is "00123"

Note that in both examples, the input string s is first converted to an integer using the Integer.parseInt() method. If the input string is not a valid integer, the parseInt() method will throw a NumberFormatException.

I hope this helps! Let me know if you have any questions.