```
public class ApologyMessageGenerator {
  public static void main(String[] args) {
    // Get user input
    Scanner scanner = new Scanner(System.in);
    System.out.println("Please enter the client's name: ");
    String clientName = scanner.nextLine();
    System.out.println("Please enter the date and time of the appointment: ");
    String appointmentTime = scanner.nextLine();
    System.out.println("Please enter your name: ");
    String senderName = scanner.nextLine();
    System.out.println("Please enter your company name: ");
    String companyName = scanner.nextLine();
```
```
    // Generate message
    String message = "Subject: Apology for Cancelling Dog Walking Service\n\nDear " + clientName + ",\n\nI am writing to sincerely apologize for cancelling the dog walking service that was scheduled for " + appointmentTime + ". I understand that you rely on our services to ensure that your furry friend gets the exercise and attention they need, and I deeply regret that we were unable to fulfill our commitment to you.\n\nPlease know that we understand the inconvenience that cancelling our service has caused you, and we take full responsibility for the situation. Our team prides itself on reliability, and we understand that we fell short of your expectations on this occasion.\n\nWe are taking immediate steps to ensure that this does not happen again in the future. Our team will be implementing a new system to prevent scheduling conflicts and ensure that all appointments are kept. Additionally, we will be conducting ongoing training to make sure our staff is fully equipped to handle any unexpected situations that may arise.\n\nOnce again, I would like to apologize for the inconvenience we caused you and your furry friend. We value your business and appreciate your understanding. If you have any questions or concerns, please do not hesitate to contact us.\n\nThank you for your patience and understanding.\n\nSincerely,\n" + senderName + "\n" + companyName;
    
    // Print message
    System.out.println(message);
  }
}
```
public class ApologyMessageGenerator {
  public static void main(String[] args) {
    // Get user input
    Scanner scanner = new Scanner(System.in);
    System.out.println("Please enter the client's name: ");
    String clientName = scanner.nextLine();
    System.out.println("Please enter the date and time of the appointment: ");
    String appointmentTime = scanner.nextLine();
    System.out.println("Please enter your name: ");
    String senderName = scanner.nextLine();
    System.out.println("Please enter your company name: ");
    String companyName = scanner.nextLine();
    
    // Generate message
    String message = "Subject: Apology for Cancelling Dog Walking Service\n\nDear " + clientName + ",\n\nI am writing to sincerely apologize for cancelling the dog walking service that was scheduled for " + appointmentTime + ". I understand that you rely on our services to ensure that your furry friend gets the exercise and attention they need, and I deeply regret that we were unable to fulfill our commitment to you.\n\nPlease know that we understand the inconvenience that cancelling our service has caused you, and we take full responsibility for the situation. Our team prides itself on reliability, and we understand that we fell short of your expectations on this occasion.\n\nWe are taking immediate steps to ensure that this does not happen again in the future. Our team will be implementing a new system to prevent scheduling conflicts and ensure that all appointments are kept. Additionally, we will be conducting ongoing training to make sure our staff is fully equipped to handle any unexpected situations that may arise.\n\nOnce again, I would like to apologize for the inconvenience we caused you and your furry friend. We value your business and appreciate your understanding. If you have any questions or concerns, please do not hesitate to contact us.\n\nThank you for your patience and understanding.\n\nSincerely,\n" + senderName + "\n" + companyName;
    
    // Print message
    System.out.println(message);
  }
}