Update messages to give Gopher a unique personality

The current messages sent by gopher makes him sounds like a robot, which
makes the application quite monotonous, this may reduce user experience
because the interactions are not very entertaining

Hence, some of the messages are rewritten to make sure that Gopher's
messages are more friendly to the user, so as to enhance overall user
experience

src/main/java/gopher/Gopher.java

@@ -144,7 +144,7 @@ public static String executeUpdateTaskCommand(String userInput) {
         try {
             String[] tokens = userInput.split(" ");
             if (tokens.length < 2) {
-                return "Update command cannot be empty...\nPlease try again...";
+                return "I don't know how you want the task to be updated\nPlease try again...";
             }
             taskList.update(tokens);
             return "Hi I have updated this task for you already!";

src/main/java/gopher/exception/UnknownCommandException.java

@@ -12,7 +12,7 @@ public UnknownCommandException(String command) {
 
     @Override
     public String getMessage() {
-        return "Unknown Command: "
+        return "Sorry, but I can't recognize this command: "
                 + this.command
                 + "\nPlease try again...\n\n";
     }

src/main/java/gopher/ui/UI.java

@@ -12,15 +12,19 @@ public class UI {
      * Get the greeting message to show to the user
      */
     public static String getGreetMessage() {
-        return "Hi, welcome to Gopher!\n"
-                + "Here are the available commands:\n"
+        return "Hi, nice to meet you! I am Gopher!\n"
+                + "I will be your task managing assistant for today!\n"
+                + "If you want me to handle any task-related issues, here are the available commands:\n\n"
                 + """
-                1. todo/deadline/event - Create event of these types
-                2. mark/unmark X - Mark X-th task as done/not done
-                3. find [keyword] - Find matching tasks based on keywords
-                4. delete X - Delete X-th task
-                5. list - List out the current tasks
-                6. bye - End the interaction
+                1. todo [name] - Create a todo task
+                2. deadline [name] /by [due date] - Create a deadline that due by the given date
+                3. event [name] /from [start date] /to [end date] - Create an Event with specified start and end dates
+                4. mark/unmark X Y Z... - Mark tasks at position X Y Z as done/not done
+                5. find [keyword] - Find matching tasks based on keywords
+                6. delete X Y Z - Delete tasks at position X Y Z
+                7. list - List out the current tasks
+                8. update X [name] [fields] [detail] - update task at position X with the specified name and fields
+                9. bye - End the interaction
                 """;
     }
 
@@ -30,7 +34,7 @@ public static String getGreetMessage() {
      * @param tasks TaskList object to be printed
      */
     public static String getTaskListMessage(TaskList tasks) {
-        return String.format("You currently have %d %s in the list\n%s",
+        return String.format("You currently have %d %s in the task list\n%s",
                 tasks.getSize(),
                 tasks.getSize() == 1 ? "task" : "tasks",
                 tasks);
@@ -42,7 +46,7 @@ public static String getTaskListMessage(TaskList tasks) {
      * @param tasks TaskList object containing all the matched tasks
      */
     public static String getMatchedTasksMessage(TaskList tasks) {
-        return String.format("Found %d matching %s in your list:\n%s",
+        return String.format("I have found %d matching %s in your task list:\n%s",
                 tasks.getSize(),
                 tasks.getSize() == 1 ? "task" : "tasks",
                 tasks
@@ -55,7 +59,7 @@ public static String getMatchedTasksMessage(TaskList tasks) {
      * @param task     task to be added
      */
     public static String getAddTaskMessage(Task task) {
-        return "Got it! I have added this task:\n" + task;
+        return "Got it! I have added this task for you:\n" + task;
     }
 
     /**
@@ -64,7 +68,7 @@ public static String getAddTaskMessage(Task task) {
      * @param task task to be marked as done
      */
     public static String getMarkAsDoneMessage(Task task) {
-        return String.format("Nice! I've marked this task as done:\n%s\n", task);
+        return String.format("I've marked this task as done:\n%s\nWell done! Keep up the good work!", task);
     }
 
     /**
@@ -101,26 +105,30 @@ public static String getUnknownCommandWarning(UnknownCommandException e) {
         return e.getMessage()
                 +
                 """
-                    Current Supported Commands:
+                    Currently I can understand the following commands:
                         1. todo - Create a ToDo Task
                         2. deadline - Create a Deadline Task
                         3. event - Create an Event Task
-                        4. mark - Mark a task as done
-                        5. unmark - Mark a task as not done
+                        4. mark - Mark tasks as done
+                        5. unmark - Mark tasks as not done
                         6. find - Find tasks based on keywords
-                        7. bye - Exit the chatbot
+                        7. update - Update a task with provided information
+                        8. delete - Delete tasks from the task list
+                        9. bye - Exit the chatbot
 
-                    Note: The command is case-insensitive,
+                    Note that the command is case-insensitive,
                     as long as the input characters match,
-                    the chatbot would be able to respond to the given command""";
+                    I would be able to respond to the given command""";
     }
 
     /**
      * Get the helping message when user inputs invalid date.
      */
     public static String getInvalidDateWarning() {
-        return ("Oops...Seems like you have passed in invalid date...\n"
-                + "Please try again with valid date and correct format...\n"
-                + "Current accepted date format: YYYY-MM-DD or YYYY-MM-DD hh:mm");
+        return ("Oops...Seems like you have provided me an invalid date...\n"
+                + "Please try again with a valid date in correct format...\n"
+                + "Currently I can read date inputs in the following formats:\n"
+                + "    1. YYYY-MM-DD\n"
+                + "    2. YYYY-MM-DD hh:mm");
     }
 }