(Rename files) Suppose you have a lot of files in a directory named Exercisei_j, where i and j are digits. Write a program that pads a 0 before i if i is a single digit. For example, a file named Exercise2_1 in a directory will be renamed to Exercise02_1. In Java, when you pass the symbol * from the command line, it refers to all files in the directory (see Supplement III.V). Use the following command to run your program: java Exercise12_28 *

Sure, I can help you with that! Here's the Java code to rename the files in the directory:

import java.io.File;

public class Exercise12_28 {
    public static void main(String[] args) {
        String directoryPath = ".";
        if (args.length > 0) {
            directoryPath = args[0];
        }
        File directory = new File(directoryPath);
        if (!directory.isDirectory()) {
            System.err.println(directoryPath + " is not a directory");
            return;
        }
        File[] files = directory.listFiles();
        for (File file : files) {
            String name = file.getName();
            if (name.matches("Exercise\\d_\\d.*")) {
                String[] parts = name.split("_");
                String newName = "Exercise" + String.format("%02d", Integer.parseInt(parts[0].substring(8))) + "_" + parts[1];
                File newFile = new File(directory, newName);
                if (file.renameTo(newFile)) {
                    System.out.println(name + " renamed to " + newName);
                } else {
                    System.err.println("Failed to rename " + name);
                }
            }
        }
    }
}

To run this program, you can compile it with `javac Exercise12_28.java` and then run it with `java Exercise12_28 *` to rename all files in the current directory. You can also specify a different directory path as the command-line argument.

This program uses regular expressions to match file names that start with "Exercise" followed by a single digit, an underscore, and another digit, and then renames those files by padding the first digit with a 0 if necessary. It also handles errors if the file cannot be renamed.