Add Level 8. Dates and Times.

Added logic in Deadline class to handle date recognition.
Added empty function in Task class for inheritance in Deadline class.

src/main/java/Deadline.java

@@ -1,13 +1,48 @@
+import java.time.LocalDate;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+import java.time.format.DateTimeFormatter;
+
 public class Deadline extends Task {
     protected String by;
+    protected LocalDate dateBy;
 
     public Deadline(String description, String by) {
         super(description);
         this.by = by;
     }
 
+    @Override
+    public void stringToDate() {
+        Pattern datePattern = Pattern.compile(
+                "^((2000|2400|2800|(19|2[0-9])(0[48]|[2468][048]|[13579][26]))-02-29)$"
+                        + "|^(((19|2[0-9])[0-9]{2})-02-(0[1-9]|1[0-9]|2[0-8]))$"
+                        + "|^(((19|2[0-9])[0-9]{2})-(0[13578]|10|12)-(0[1-9]|[12][0-9]|3[01]))$"
+                        + "|^(((19|2[0-9])[0-9]{2})-(0[469]|11)-(0[1-9]|[12][0-9]|30))$");
+        Matcher dateTimeMatcher = datePattern.matcher(this.by);
+
+        if (!dateTimeMatcher.matches()) { // if datetime doesn't match, do nothing
+            this.dateBy = null;
+        } else {
+            Pattern dateTimePattern2 = Pattern.compile(
+                    "(\\d{4})-(0[1-9]|[12][0-9]|3[01])-(0[1-9]|1[0-2])"); // YYYY-MM-DD
+            Matcher dateTimePattern2Matcher = dateTimePattern2.matcher(this.by);
+            dateTimePattern2Matcher.matches();
+            int day = Integer.parseInt(dateTimePattern2Matcher.group(3));
+            int month = Integer.parseInt(dateTimePattern2Matcher.group(2));
+            int year = Integer.parseInt(dateTimePattern2Matcher.group(1));
+            this.dateBy = LocalDate.of(year, month, day);
+        }
+    }
+
     @Override
     public String toString() {
-        return "[D]" + super.toString() + " (by: " + by + ")";
+        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MMM d yyyy");
+        if (dateBy == null) {
+            return "[D]" + super.toString() + " (by: " + by + ")";
+        } else {
+            String formattedDate = this.dateBy.format(formatter);
+            return "[D]" + super.toString() + " (by: " + formattedDate + ")";
+        }
     }
 }

src/main/java/Jarvis.java

@@ -297,6 +297,7 @@ public static void main(String[] args) {
                     String taskDescription = deadlineMatcher.group(2);
                     String by = deadlineMatcher.group(3);
                     newTask = new Deadline(taskDescription, by);
+                    newTask.stringToDate();
 
                 } else { // if "event" is entered
                     String taskDescription = eventMatcher.group(2);

src/main/java/Task.java

@@ -11,6 +11,8 @@ public void setDone(boolean done) {
         this.isDone = done;
     }
 
+    public void stringToDate() {}
+
     public String toString() { // generates the string of marking and task
         String marking = "";
         if (this.isDone) {