(Replace words) Suppose you have a lot of files in a directory that contain words Exercisei_j, where i and j are digits. Write a program that pads a 0 before i if i is a single digit and 0 before j if j is a single digit. For example, the word Exercise2_1 in a file will be replaced by Exercise02_01. 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_27 *

Certainly, I can help you with that. Here's some sample code that should do what you're asking for:

import java.io.File;

public class Exercise12_27 {
    public static void main(String[] args) {
        if (args.length == 0) {
            System.out.println("Please specify a directory or use '*' to apply to all files in the current directory.");
            return;
        }

        String directory = args[0];
        File dir = new File(directory);
        if (!dir.isDirectory()) {
            System.out.println("Invalid directory specified.");
            return;
        }

        File[] files = dir.listFiles();
        if (files == null) {
            System.out.println("Could not retrieve files in specified directory.");
            return;
        }

        for (File file : files) {
            if (file.isFile()) {
                String fileName = file.getName();
                if (fileName.startsWith("Exercise") && fileName.matches(".*\\d_\\d.*")) {
                    String[] parts = fileName.split("_");
                    String i = parts[0].substring(8);
                    String j = parts[1].substring(0, 1);
                    if (i.length() == 1) {
                        i = "0" + i;
                    }
                    if (j.length() == 1) {
                        j = "0" + j;
                    }
                    String newFileName = "Exercise" + i + "_" + j + fileName.substring(fileName.indexOf('.'));
                    File newFile = new File(directory + "/" + newFileName);
                    if (file.renameTo(newFile)) {
                        System.out.println("Renamed file " + fileName + " to " + newFileName);
                    } else {
                        System.out.println("Could not rename file " + fileName);
                    }
                }
            }
        }
    }
}

You can save this code to a file named Exercise12_27.java and then compile and run it using the following commands:

javac Exercise12_27.java
java Exercise12_27 *

This will execute the program on all files in the current directory that match the pattern Exercisei_j, padding a 0 before i and j if they are single digits. The program will output the names of any files that it successfully renames.